Here's another batch of 12 bugs I've come across or that others pointed out to me for Flight 3. Not sure how many were already reported but here's the video with all the steps for each bug: https://www.youtube.com/watch?v=ABfvA0MnxGA
#1 - In Halo 2 Anniversary Forge only, the Brown and Pink team have the wrong colors in game. They become Lime and Cyan on the scoreboards and HUD but armor color is still correct and it still says Brown and Pink. This is likely caused by the team color menu taking the same settings from the Halo 4 forge menu which does have Lime and Cyan team in the exact spots where Brown and Pink team are in Halo 2 Anniversary Forge.
#2 - On the sandbox maps in Halo 2 Anniversary Forge (Skyward, Nebula, Awash), the Fusion Coils when placed down will have Fixed physics no matter what you set them to. They simply won't budge anymore even if they're set to Normal physics. Also, there are several other objects in Forge (these happen on any map) where the physics are also wrong. Several crates, containers, and building blocks when set to Normal physics end up having Fixed physics no matter what you do.
#3 - On the Halo 3 mission Crows Nest, after you clear the hangar near the beginning, the Pelican that's supposed to take off with Marines never does. It seems like it's waiting for enough marines to get into it before it takes off but on MCC, it seems like the correct amount of marines needed for it to take off never spawn and therefore the Pelican never takes off.
#4 - In Halo 4 multiplayer modes, on the map Ragnarok, there's a very small specific spot on the back of the map where if you fly a Banshee into it, there'll be no engine sound at all for the Banshee. I have not had the chance to test it on older versions of Halo 4 to verify whether it's exclusive to MCC or not.
#5 - On the mission Dawn in Halo 4, shortly after the 2nd rally point, there's a point where after you see a window of outer space and clear out some covenant, you go down a flight of stairs. To the right of the stairs, there's a wall there that's totally green.
#6 - The Universal Bump And Jump controls are incorrect for Halo 2 Anniversary Multiplayer specifically. The Left Bumper controls for vehicles (eg Banshee Flip) have been incorrectly mapped to the Right Bumper, so you have to press the Right Bumper now to do banshee flips or brakes in vehicles. This only affects Halo 2 Anniversary, Universal Bump and Jump seems to function fine for other Halo games.
#7 - In Halo CE Anniversary graphics, there are simply no shadows at all for anything. The shadows display just fine in classic graphics, but in Anniversary they're completely missing for everything.
#8 - On the bridge of the Pillar Of Autumn in Halo CE Anniversary graphics, once you pass a certain point as you're entering the bridge, the lighting suddenly becomes extremely bright but reverts to normal if you walk back past that point. The difference is very noticeable and looks like you're flipping a light switch on and off.
#9 - In Halo CE Anniversary graphics, occasionally in 3rd person (other player's perspectives), you won't be able to see the ammo count on Assault Rifles. It will simply be a blank screen. This doesn't seem to occur 100% of the time though and seems to happen randomly every now and then.
#10 - On the mission Oracle in Halo 2 classic graphics, the tank full of mini flood infection forms at the very beginning will sometimes have these forms float out of the tank and then back in.
#11 - In Halo 2 Anniversary graphics for campaign, the Scorpion tank treads will spin in the wrong direction if you're moving in one direction (eg backwards) and then quickly switch to the other direction (eg forwards) without stopping. Basically you'll end up driving a Scorpion tank forward with the tank treads spinning in reverse. This only affects Anniversary graphics.
#12 - This one I know people have been mentioning for awhile, but I've compiled the exact steps to reproduce the issue if no one has mentioned any clear steps yet. On the Halo 2 mission Regret, there's a Phantom that flies in towards where the 1st gondola is to drop off a pair of Hunters. If you go through the mission fast enough and skip one of the checkpoints that you get while you're in the 2nd room full of enemies after you exit the first room, and then clear all the enemies at the 1st gondola platform fast enough and still manage to avoid a checkpoint, then once the phantom flies in to drop off the Hunters, as it touches down, it will just simply vanish and the game acts like you've cleared out the Hunters. This is confirmed to work on all versions of MCC currently but does not affect any older version of Halo 2 (Xbox, Vista).
Hope the video and this list helps!