The biggest spells like Expropriate and other Time Walk variants
Krovikan Horror has an effect that's been since discontinued, where it cares about the order of cards (notice that it says a summon/creature card directly above it) in your graveyard, something that's a bit difficult to keep track of in a real game
The only thing is the bounce deck likely wants to be aggressive and win early with a lot of lore gain from bouncing things
Bitterblossom definitely deserves an honorable mention, of course
Creatures that enter with -1/-1 counters on them become effectively immortal when you have Mikaeus on the field, so all you need then is a sacrifice outlet like Phyrexian Altar and you form a loop that lets you draw infinite cards and create infinite mana (until you deck yourself)
I increased the budget for this project due to the nature of the challenge, and it's the only entry in the series where the cost is increased rather than decreased