History YMMV / StarCraftIICoopMode

** There are a variety of units that never see any action in this game mode whatsoever, or abilities that don't have much of a presence, such as the Predator, or the Infestor's Neural Parasite (the Aleksander does have the Neural Parasite ability, but it's tied to its anti-air attack, which damages its targets over time).

** Artanis used to get flak in general for essentially being a SkillGateCharacter: easy to pick up and use, but otherwise underwhelming in almost every way. His army units are good, but not great at their roles compared to other commanders' arsenals, and they all suffer from relatively low damage output. His calldowns are considered some of the weakest in the game; Shield Overcharge and Solar Bombardment are crippled by their glacial cooldowns, his power field is good for replacing units and not much else, and Orbital Bombardment is just embarrassingly bad in general (especially since Karax has the ''exact same calldown'', only better in nearly every way). What usage he ''did'' have in lategame more or less boiled down to being brought along to use his ''Guardian Shell'' to cheese mechanics based on dealing high burst damage, an ability that requires precisely ''zero'' actual involvement on his player's part. He got a massive buff on all fronts in 4.2.4, which mostly saved him.

* CheeseStrategy: Mengsk's Earthsplitter Ordinance allow him to clear certain maps with almost contemptuous ease by simply bombing objectives into a smoking crater from long range. Rifts to Korhal is particularly infamous, as there's a spot on the map where he can set up a battery of Earthsplitters that can hit every Void Shard that spawns while never getting attacked by Amon's forces. All his ally has to do once he's set up shop is hunt down the bonus objectives and fend off attack waves (and even the latter might not be necessary if the Mengsk player is good at leading the target with Contaminated Strike). Similarly, he can cheese Scythe of Amon by clearing far Slivers with bunkers and nukes before using Earthsplitters to kill the two closest to his base.

** "Buy Buy Buy (Buy Buy)" requires Tychus to get all the gear for all five Outlaws before the 20 minute mark. In regular play, you'd be lucky to fully upgrade three of them by that point due to the finite resource income; you pretty much have to skip basically everything else that demands resources or get your teammate to leave (which gives you access to their resources) to even stand a chance of getting this. And even with extremely tight macro and an optimized build order, you'll likely only get the achievement with ''less than 20 seconds to spare''.

*** Propagators, spawned by the Mutator of the same name, quickly gained infamy among players for effectively being an instant GameOver if not dealt with appropriately. When a Propagator comes in contact with one of your units or structures, it will OneHitKill its target before turning it into another Propagator. And no, your {{Hero Unit}} are just as vulnerable to this trick. If not handled properly, this can result in a massive snowball of Propagators that will destroy your army in seconds, followed by your base. Stukov in particular is especially weak against these enemies, due to his massed infected Terrans providing them with ample fodder, and he himself has relatively limited means of dealing burst damage from range, as well as Stetmann due to his Stetellites still being vulnerable to their replication attack. Thankfully, Propagators themselves are still vulnerable to crowd-control effects like Vorazun's Time Stop, or Kerrigan's Immobilization Wave, which can allow certain commanders to shine in this particular scenario, though it will be a very different story if the [[RandomEffectSpell "Chaos Studios"]] Mutation rolls Propagators while you're playing a commander that's ''not'' good against them...

*** Propagators, spawned by the Mutator of the same name, quickly gained infamy among players for effectively being an instant GameOver if not dealt with appropriately. When a Propagator comes in contact with one of your units or structures, it will turn into another Propagator; if you can't kill them off at range, this will result in your entire army being destroyed in seconds, followed by your base. Even ''hero units'' aren't immune to the effect. These guys can effectively hard-counter certain commanders, like Stukov and Zagara, who simply don't have any options to deal with them, resulting in some serious CharacterSelectForcing for Mutations that involve this Mutator. And if the [[RandomEffectSpell "Chaos Studios"]] Mutation rolls Propagators while you're playing a commander that's not good against them, you might as well restart.

** Certain enemy attack waves make life hell for players. Any of the three "Protoss Armada" compositions (colloqually referred to as "Skytoss") will send massive fleets variably consisting of Oracles, Phoenix, Void Rays, Carriers, and Tempests. For the Terrans, Dominion Battlegroup ("Skyterran") will send fleets of Ravens, Banshees, Vikings, Liberators, and Battlecruisers. Such a mixed force, especially in the number present on higher difficulties, would crush even pro-level melee players, but consider that ''Co-op'' commanders have more limited tech trees; for some of them, they may simply have no feasable way to regularly fend off large numbers of top-tier air units. Terrans also have "Shadow Tech", which basically means their most annoying burst damage units -- early waves will be Reapers, who can very quickly destroy structures, Cyclones to kite armored units, Liberators to siege your units with artillery from above, Battlecruisers to fire Yamato Guns at eveything, and Ravens to unleash Seeker Missiles on your deathball.
** Not to be outdone, the Zerg have their own lethal unit composition, Explosive Threats -- their attack waves will consist of large numbers of Banelings and Scourge, which will melt pretty much any army no matter what commander you are or what units you're using. When they're gone, you get to deal with Zerglings, Aberrations (who deal bonus damage to armored units), and Vipers (who retain their Disabling Cloud and Parasitic Bomb abilities from melee play, as well as Abduct to easily get your valuable units killed), a unit composition that can quickly shred battered and weakened armies left over from the wave of suicidal units. It's quite telling that Explosive Threats had to be nerfed by replacing some of the Scourges in attack waves with Mutalisks to reduce their AntiAir damage output because it was ''just that good'' at utterly murdering air units.

** The bonus objective of "Part and Parcel" provides to rest from the wicked either, as the first target spawns pretty early in the mission and behind enemy lines. If the way isn't cleared in time, the first train will escape. There isn't much time in between the first and second trains' departures either, and the first train usually leaves in time with the fight with the first Hybrid boss.

*** Mengsk commanders tend towards Toxic Tyrant, as its benefits greatly power up his Contaminated Strike calldown and make Earthsplitter Ordinance (which is already pretty good) more viable and generates mandate when troopers are manning those structures. The drawback is that he loses his Nuclear Annihilation calldown, but given that it costs 100 Mandate to use, it was AwesomeButImpractical in the first place, and his Dogs of War calldown is just as effective.

** At one point, Zeratul's Shieldguards had a bug with their Reflective Shield ability (deflects enemy's attack): it was possible to deflect attack of the [[GreyGoo Propagator]]... [[https://www.youtube.com/watch?v=QxHN-MXrJ2I resulting in it it turning itself into a Propagator under player's control]]. The bug was quickly patched out.