I have a suggestion for The Wall.
Some shiftable barrels on the far right (stairs) side.
More characters can attempt it now, since you'd no longer need a rocket launcher, which I usually don't find in time for The Wall. This also allows weapon-limiting challenges, like AoMr and AoB to try as well (although you'd need a good stash of healing kits for AoB).
The only issue here I can see is that the player is no longer in danger of blowing up the goodies on the far left side with poorly aimed rockets. On the other hand, if you're not taking on The Wall with a rocket launcher, it's probably going to be a lot harder for you to win/survive anyway.