Halo 2 on Legendary is a pain. I know you said in your OP you thought you might as well have done LASO, but that is 1000x worse, trust me.

I can carry you through the level sometime, if you want. I’ll test the invulnerability glitch on co-op at some point and see how well it works. My guess is it won’t work due to co-op teleporting.

You can make yourself invulnerable on the Oracle level (at least for the last fourth or so of it) by activating the lift to the room where you cut the cables while off the lift, then activating it again so it comes back down, and letting it squish you. It’ll yeet you to the top of the lift and you’ll be invulnerable for the rest of the level. I don’t know how well it works in co-op though.

It was a glitch that originated in the Halo 2 Vista port and carried over to the MCC since they based it off the Vista port.