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October 25, 2021

Transmission 11: Co-op

TR11: A plan for co-op
Transmission 11
  A plan for co-op

In this post, I will look again at Co-op, and more specifically at one way how I could imagine putting it all together. Speculating and thinking about individual features is a lot of fun, but here I want to take a more high-level look and see how a comprehensive plan for co-op could look and what would even be its goals. Some of the discussed topics are more general and interesting even outside of co-op or the RTS genre.


StarCraft II Co-op turned out to be a big success even though it wasn't excepted to be played for more than a couple dozen hours. Later it was greatly improved with new maps, commanders, enemy AI, new modes (weekly & custom mutations, and Brutal+) and progression systems (mastery, prestige, ascension). Despite all those improvements and the mode's success, I believe it still has the most potential for both growth and improvement in future games.

Previously, I looked at various individual features that could be tried or improved in Co-op:

  • TR04 (survival mode, asymmetric mode, stream integration, etc.)
  • TR05 (events, greater events, weekly mutations, progression, etc.)

Laying out possible options for features is great. However, it's yet another thing to choose which of these features would fit together and which to leave out. In this post, I want to look at one such plan, but first what are the goals for it?

  1. Increase gameplay variety.
    → Games are unlike each other, and something exciting can happen the next game!
  2. Provide challenge to players that are looking for it.
  3. Create a cohesive structure that can be seamlessly expanded with new content.

A place for future content

I want to touch on the last point first and make it clear that it's useful to think about how a system can be expanded later. Getting this right is especially important for free-to-play games as there are always new players coming in, and the need for content updates is higher.

After several updates, DLCs, or expansions, many games suffer from clashing mechanics and overwhelming players. A new or returning player might get confused by several progression systems, currencies, or mission lines – some of which can be outdated. If it's not clear what the player should focus on, the experience might become confusing and frustrating. New games are usually carefully tested when it comes to new player experience and good game flow. However, with the following updates, developers are trying their best to add things with the limited resources they have, and the new player experience can suffer because of that.

Increased complexity of the main screen after launch (Angry Birds 2).
While this is just a screen, it's often accompanied by cluttering of gameplay systems.

Prestiges are a good addition to StarCraft II Co-op. But if a new player that just leveled his first commander to the maximum level chooses to prestige their commander right away, the game might feel grindy. The player will likely be doing the exact same thing again as many prestiges have only a minimal impact during leveling. Prestiges were designed to add replayability for long-time players, however, a new player doesn't know that and might choose to prestige instead of trying out another commander or playing with a full commander kit on mastery levels.

Choices a new player will have after leveling up the first commander (StarCraft II Co-op)
The prestige choice might look like the most natural path of progression, but it might also feel the most repetitive.

Obsolete content can also cause issues in games. Apart from confusing players, it's also an inefficient use of development resources. Some games have to resort to removing obsolete content from the game, and then there is Destiny 2 which will remove even content that players have paid for. That's a PR nightmare. Ideally each update would improve the game in long term.

This leads us to another point, it's preferable if the goals of developers (or publishers) are aligned with the player goals. Examples of misaligned goals would be if the player progression was artificially slowed so players would buy boosts, or if a competitive game was releasing overpowered characters and nerfing them only before the next one is ready for release. In such cases the game's longevity will suffer.

To sum up, there are three things to look for: (1) the addition of new content shouldn't make the game confusing for new or returning players, (2) new content should improve the game in the long term, (3) and player and developer goals should be aligned.

Loopity loop

Now let's go back to the first point – gameplay variety – and look at the overarching structure spanning across multiple co-op games. You could think of it as being made of gameplay loops of different sizes. The point of these loops is to create a change in content, pacing, and tension. Books and movies also have a rising and falling tension, however, in games you typically find loops of all sizes and rewards increasing with the size of each loop.

What are some loops that you would be able to encounter in co-op?

  • Small gameplay loop – a macro-cycle
  • Bigger gameplay loop – defend then attack
  • 1 game size – play a game, get rewards, spend points, check unlocks
  • 2–3 game size – encounter and complete in-game event (optional, could replace bonus objective, higher challenge, and rewards that include unlocks for greater events)
  • 5–7 game size – complete a greater event (even bigger challenge and rewards, static, players can save unlocks for later)
  • Weekly size – weekly mutations provide a reason for players to come back, discuss strategies and rank commanders
  • 25-ish game size – level-up one commander
  • 3–4 months – seasons provide another reason to come back for new content and challenges. New commanders and maps could align with seasons.

Compared to SC2 Co-op, there are a few new loops – event loop, greater event loop, and seasonal loop. The last one might or might not align with commander releases. I believe the two smaller loops would add more variety to the co-op as it can get a bit stale between weekly mutations. More on this in the next section.

Event and greater event loops, and what gameplay sessions might look like

The next game

"Something cool can happen the next game" is something that has been missing in StarCraft 2 Co-op. While the mode provides a good variety through various means (random partner, map, commander, enemy race and AI, and map pattern), the game can still feel repetitive. Brutal+ greatly improves gameplay variety with random mutators, but rewards stay the same and it often feels like you either get something all right or annoying. There isn't the feeling of anticipation – what could be next?

Some inspiration could be taken from Diablo III. There is a hierarchy to encounters and excitement coming from them: elite group/boss < Treasure Goblin < Gelatinous Treasure Goblin (splits into more goblins). Encounters are randomized and can combine – leading to at times crazy situations when you pull half the map while chasing goblins. This is a variable ratio reinforcement schedule at its finest – affecting both encounters and rewards.

It would be great to have things in an RTS co-op mode that lead to similar experiences. What could be added to facilitate this feeling that something exciting can happen in the next game?

  1. Events can randomly appear in missions. These are fully optional and provide higher challenges and better rewards. Some could be challenging by themselves, others could make the game harder after completing them (e.g., enable some mutator), and some could be more like Treasure Goblins – not providing direct challenge themselves but encouraging players to extend more.
  2. Randomized rewards that could be and awarded for more rare events. These rewards could include in-game currency, experience, greater event unlocks, cosmetic rewards, or commander side-grades. I'm against incremental upgrades as seen in AoEO, but I could see a limited amount of rare side-grade upgrades working.
  3. My survival mode has solarite upgrades where you can choose one out of three randomly presented upgrades. If leaned more heavily into this design, you could get something closer to a deck-building game. For a survival mode on a single map, this adds much-needed gameplay variety. The current upgrade design isn't the best, but it's still exciting when you manage to stack +10 bonus range to turrets while playing a commander with strong static defenses. If these upgrades are meant to be exciting, there has to be at least a chance for them to be game-breaking.

Similar upgrades can be found in Orcs Must Die 3's Scramble mode (third-person wave defense) or in Alien Marauder or Age of Darkness (survival RTS games). In all cases, these choices lead to unique playthroughs while leaving players some agency. One difference is that my solarite upgrades are given for completing objectives on the map and not just progressing. That gives players reasons to venture on the map and makes offensive-focused commanders more useful. I hoped there was a similar incentive in Age of Darkness with malices and crystals where enemy waves spawn, but you can only trigger a wave early or gather a few small crystals after it's triggered.

Choose your reward from the available options (Alien Marauder)
Pretty much the same thing but with prettier UI and higher impact (Age of Darkness)
Blessings are given after each wave (up to five).
Random negative modification (malice) active for one night (Age of Darkness)
On a custom difficulty these can be permanent.

What else made you excited and motivated to play just a bit more? In Diablo, it's the unpredictability of encounters and item drops, and the loop of trying out new equipment and skills while obtaining new ones at the same time. In Civilization games, it's the "one more turn" syndrome where there is always one task that has been long underway and could be finished the next turn. Seeking closure is natural and so players are motivated to play "one more turn".


What would be the main sources of a challenge for players seeking it?

  • More difficult the highest standard difficulty
  • Weekly mutations and their backlog that can be completed
  • Events & greater events (~weekly mutation difficulty)
  • Empowered greater events (~hardest weekly mutations)
  • Survival mode (~you will most likely lose)

Typically as challenges become more difficult, the room for error becomes smaller, and the role of randomness increases – which mutators did you roll? what's the map? what commander do you and your partner have? Before you could overcome this randomness with skill, but the more challenging the mission becomes, the less randomness you can overcome. Knowing a challenge beforehand reduces the role of luck, and enables strategic planning before the game – coming up with a plan and choosing the right combination of commanders or specializations. This can be a lot of fun, and I would say this is the most "strategic" activity the majority of players will do in StarCraft II.

Because of this, more difficult challenges (greater events and weekly mutations) would be known beforehand, and players could prepare for them. Difficult challenges would be also aimed more at parties instead of random matchmaking. This again reduces randomness and makes strategic planning easier.

Basic events are less challenging, and so those could appear randomly during normal missions. They would also be optional, and so players could adjust their strategy during the mission before engaging with the event.

The map and mutators are known before the game for weekly mutations in StarCraft II Co-op
This reduces randomness and lets players strategize.

Let's approach this topic by looking at the game's unpredictability. We typically want some unpredictability, but it cannot be too low or so high that player actions don't matter.

Content that's not challenging can become too predictable, and so there is a role for in-game randomness (RNG) to spice up the gameplay and increase gameplay variety (e.g., random events, AI, map, mutators). However, if we increase the difficulty, the challenge combined with RNG could mean that the game becomes too unpredictable – it's decided by the RNG, and players lose the power over the game's outcome. For more challenging content it's better to reduce or remove RNG and let the unpredictability come from player execution and strategy.

From a low to high challenge:

  1. Casual co-op (low challenge, RNG is good and increases gameplay variety/unpredictability)
  2. Co-op challenges (medium to high challenge, RNG should be reduced)
  3. Speed-running or competitive modes (maximum challenge, RNG can hinder gameplay)

Recommended RNG here is inversely proportional to challenge. However, that's just a broad recommendation and there are always exceptions. In the end, it's all to have good gameplay variety while keeping player agency. There can be fun casual games with no RNG, competitive games like Hearthstone with a great deal of RNG (for better or worse), or Fischer Random Chess with just initial board input randomness (to combat the excessive focus on memorization of openings and build-orders).

Fisher Random Chess randomizes the positions of back-rank pieces and mirrors the positions for the opponent

Mission variety

It can be difficult to have enough content that can be played with commanders. SC2 Co-op eventually reached 15 unique missions with randomized patterns, enemy factions, and the maps could be further enhanced with various mutators in different modes (weekly & custom mutations or Brutal+). Let's see what other approaches could help the effort for more content playable with co-op commanders.

  • When creating campaign missions, make it as easy as possible to later port the mission to co-op. While a co-op campaign would be great, every mission would likely not support all present and future co-op commanders, as that would limit the campaign and commander design too much.
  • Have an easy way for mapmakers to let players use their purchased and leveled commanders in custom maps. The system would automatically get which commanders the player has and what's their progression status. No experience would be granted for custom maps, but it would make things easier for mapmakers (thus better and more content) and make purchasing and leveling commanders more meaningful.
  • If there is a variety mode that changes rules each week, co-op commanders could be playable during some rotations.
  • Having good challenging content with interesting rewards will be enough for some players. I believe the addition of events, greater events, and some kind of survival mode would help here.
  • Increased randomization (events & bonus objectives, attack wave timing and spawn points, more diverse hybrids/heroic units, experiment with dynamic weather effects like rain, snow, desert).

A plan for Co-op

With all that out of the way, let's finally look at one possible plan for co-op. This plan builds upon SC2 Co-op, is by no means perfect, and could be structured differently – for example with more focus on the survival mode, 2v1, or something wholly different. There might better ways to approach it, and I'm looking forward to seeing what other games will do. SpellForce 3 will be adding a co-op system, and there might be something to learn from Overwatch 2's Co-op missions as well.

1. More challenging highest standard difficulty. Together with the challenge of basic events, this would make the baseline co-op experience better for experienced players. The goal is to push the need for different modes that provide a challenge a bit further.

Standard difficulty cannot scale to the same difficulties as Brutal+, but there is a design space for some difficulty increase. This could include stronger and more upgraded earlier waves, hybrids gaining new or improved abilities, randomized spawn points, an equivalent to harassing Nyduses and Warp Prisms – similarly how Terran AI harasses with nukes, or heroic units like Leviathans being a part of later attack waves. Not showing attacking wave indicators is another possibility, but that might not fit well into co-op.

The downsides of having increased maximum difficulty for standard missions are higher fragmentation of the matchmaking queue if there are more difficulties, or making it harder to advance to the next difficulty if there aren't more difficulties. This could be addressed with an improved system for mixed difficulties, which doesn't work that well in StarCraft II.

Attacks on the Void Launch mission can be scary when waves combine and include heroic units like Motherships
(StarCraft II Co-op)

2. Increased mission randomization. This is to increase gameplay variety for normal missions. Randomization could affect events, bonus objectives, attack wave timings and spawn points, or enemy heroic units. More commander-to-commander interactions can have a similar effect in the random queue. It would be also interesting to explore a way to start a map at different times of day and weather (rain, snow, desert). That could be a purely visual effect – either random or tied to certain mutators and events (e.g., Blizzard → snowing). This should make the experience more distinct and memorable.

3. Randomized rewards are something I enjoy in action RPGs like Diablo, and it could lead to more excitement about rewards and more interesting progression. It's an understatement to say that you are not very excited to get your 59.5k XP after a mission in SC2. However, it's important to strike a good balance between what's randomized and what isn't. Randomized rewards can be tricky to get right.

I imagine each mission would provide a consistent reward the same way as in SC2 Co-op, this would include experience and in-game currency if there is any. Events, greater events and other challenges would also grant randomized rewards (cosmetics, bonus XP and currency, commander side-grades, etc.). Granted that there would be an alternative way to get a specific commander side-grade if you were unlucky and wanted it badly.

4. Events and Greater Events. I talked about them previously and in this post, and I see them as the main way to increase gameplay variety, create rising and falling tension and difficulty between games, and in the case of basic events also increase unpredictability. The main distinction is that basic events can appear randomly during normal missions, while greater events are semi-randomized challenges that a player can unlock and complete at any time when in a party. Greater events provide a higher challenge and better rewards. There could be empowered greater events for even more challenge and rewards if more unlocks were spent on them.

There is a lot to talk about, but one question is particularly interesting. Would requiring a party for greater events be beneficial? On one side it's a bit bothersome having to talk to someone and form a party, but on the other side, it leads to a better social experience. The goal would be made to make this as painless as possible. First, unlocks for unlocking a greater event are provided by the party leader, and so a person helping is rewarded without spending any of his unlocks. Players are encouraged to help others.

Second, unlocks can be saved up. This means there is no pressure to party up when you don't feel like it. The unlocks can be spent later when a friend comes online. This also makes solo play in random matchmaking more meaningful as it impacts when you play later in a party. And it naturally shifts these more difficult challenges to when you are in a party.

For these reasons I think requiring a party for greater events could be beneficial. Automated dungeon finders in MMOs like World of Warcraft certainly made it a lot easier for players to enjoy the content, but at the same time, it also hurt the social side of the game which is the main selling point of MMOs. I think greater events could incentivize social interaction, and that would have a positive effect on the game in the long term. This is also why I argued for making it as easy as possible to go from talking to someone outside of the game to playing together (with links). Though I cannot be sure that requiring a party would have the desired effect. Plus it depends on other factors like other social systems, how often would you engage with greater events or what are rewards. If players engaged significantly less with the content because of the party requirement, then that would be a problem.

Automated dungeon finder in World of Warcraft
Great for getting to play the content, less good for socializing in the game

5. Weekly mutations and backlog. Weekly mutations have been a great addition to SC2 Co-op and it would be great to see them continue. One nice thing to add would be a list of previous mutations. It would mark which mutations you have completed, and let you play any of them when in a party. You could be given a reward for completing the ones you haven't already, but the reward would be lower than when completing it in its week. Still, that would be a lot of content for people who weren't playing each week.

I also previously suggested letting players repeat the current weekly mutation with unique commanders few times for limited additional rewards.

Weekly mutations could be promoted on the main screen

6. Survival mode is something that shouldn't be missing from Co-op. But there are multiple ways how it might be implemented. It could be part of greater events, an optional part of certain missions, or a separate mode altogether.

Another question is what exactly would be the goal? Is it to survive a certain amount of waves as in They are Billions and other recent survival RTS? Get the best score with infinite ever more difficult waves? Or complete as many side objectives while defending? My demo for SC2 Co-op was with infinite waves, but I also like the idea of a fixed amount of waves and side objectives to complete. That would enable some sort of dynamic difficulty by players choosing what they will try to complete, and increase variety by randomizing these objectives.

7. Game passes/seasons could be a part of Co-op. The main idea is to add something new for players to enjoy on a scale of 3–6 months. These might or might not align with commander and map releases. They could include new rewards, (greater) events, and other gameplay modifications which might or might not stay after the season ends (similarly to leagues on Path of Exile).

There could be additional monetization beyond purchasing a commander, but that would be tied with other modes like competitive, and I don't want to speculate on that here.

other notes

  • I didn't mention streaming integration. While I think it's great to have, it's not something defining co-op.
  • Asymmetric 2v1 with co-op commanders could be a lot of fun. If there was enough willpower to try it, I would lean more towards trying to seamlessly integrate it into standard co-op than creating a whole separate mode.
  • I didn't include anything similar to Brutal+, though (greater) events would likely include mutators. I don't think the mode is bad, but there are challenges with it in StarCraft II. This includes using mutators that were designed for something different, not knowing the mutators beforehand, and lower Brutal+ difficulties being more annoying than challenging. A lot of it could be improved, but right now I prefer the event-greater event system more.
  • There are a lot of ideas about other modes with mutators like my challenge mode, scaling modes where each mission adds mutators (or you choose from limited options), or player-created mutation challenges that can be completed by anyone or selected players. These are very interesting as well and could be used if co-op was structured another way.


This has been a long post, and I think I have touched on a lot of interesting topics. The goal here wasn't to show a recipe how to create a co-op, but instead to see what such recipe should even do, and then try to formulate something that I could imagine working. I don't expect the actual co-op mode to look anything like this, but hopefully the post was useful and interesting. Thank you for reading.

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