Something I did for fun once was running NG+ challenge mode with 2 monsters. Maybe this could be fun for the standard and/or NG+ challenge modes.

I managed to (technically) get past the kaiba fight, but I was too damaged to have any hope of getting through yugi.

The team is triple blue eyes with each of them having a polymerization, a red medicine, and a deal of phantom. I've also experimented with replacing one of the red medicines with a blue medicine but either way it'll take godly rng to get through the entire thing.

The route I was going for was as follows:

Fight #1: Chip the worms to ~1200 and then polymerize (will likely need to burn 1 heal), as long as all attacks hit you'll wipe him.

Fight #2: Burn swordstalker down and then guard/heal

Fight #3: Burn Curse of Dragon down and then guard/heal

Fight #4: Polymerize first round, try to get 1-2 kills for exp

Fight #5: Burn meteor dragon down and then guard/heal

Fight #6: kill 1 blue eyes while trying to keep all 3 blue eyes alive and reasonably healthy.

Fight #7: pray to god you can get some chip damage on Buster Blader and then polymerize. Try to kill Buster Blader and survive.

Fights 1 and 2 are pretty consistent, 3 requires you to deal exactly 3 attacks worth of dmg in the first round so you can get screwed by a crit on the 3rd attack, a miss, or any of ur guys dying since you don't have the wiggle room to heal. 4 is consistent with the polymerization, 5 is similar to 3 except you take a lot more dmg, and while the rng for 6 and 7 is even more brutal, my testing with save states (and doing some real attempts) leads me to believe the probability of a run succeeding is something in the range of 1/500, which is still kind of reasonable for a human to pull off.