* ComplacentGamingSyndrome: Good luck finding someone online who doesn't attack with Spartans in Scorpions.
* DemonicSpiders: In ''Halo Wars'' multiplayer, Gauss Hogs are this, with Gunner/Grenadier Hogs only being GoddamnedBats.
* FridgeBrilliance: Look closely on the visors of the [=SPARTANs=] on the cover, and you'll see the Arbiter and Elites. The Limited Edition cover shows the Arbiter and Elites. They're facing each other.
* GoodBadBugs: The unfinished Scarab can't kill units in cover, as hard as it tries. Put some Marines in the Covie guard tower in the middle of the map and you'll have the Scarab distracted for the rest of the level.
* MemeticMutation: [[http://oi40.tinypic.com/9sqwjq.jpg HAAH WAAW]]
* ThatOneLevel: 'Scarab'. The titular Covenant walker tank acts as a stationary turret tearing through all your troops. If you take too long it's game over, and it can take a hell of a beating. To get the gold medal you almost have to glitch.
** Arcadia and Dome of Light are also nightmarish. Arcadia forces you to play defense and offense as well as babysit blink-and-they-die transports. Dome of Light brings wave after wave of Covenant forces to your base to keep you from planting 5 mildly durable tanks. It's insanely difficult to protect the [[DemonicSpiders Hunter]] flooded base and still guard the tanks,even using leader transport powers tends to barely finish the mission.
** The level The Flood. If you thought those space zombies were hard in single player, try fighting a whole army of them ''while'' trying to destroy their colonies to weaken their largest one. Did we mention that the colonies regenerate if you take too long to destroy them all?
** Repairs. The dropships start coming faster and faster and faster and faster... [[FromBadToWorse And eventually the Covenant destroyer joins in.]]
* ThatOneSidequest: 'Running The Show' achievement requires a million points in multiplayer. This is reduced from the original three million. This represents literally hundreds of hours of play.