Most schemes will have a one-time effect, such as destroying your opponents creatures or drawing you a bunch of cards, but some are ongoing effects that will persist until someone fulfills their abandon requirement
However some people have questioned if the sticker glue might damage the card over time if it is left unpeeled
Ratchet Bomb is a sweeper that can take down more expensive things the more counters it has, and Magistrates Scepter is a potentially repeatable Time Walk effect
I had some ideas for non-traditional artifact payoffs, where Bartered Cow is technically a nonartifact you can cast with Inspiring Statuary, but that quickly descends into nonsense territory
Some version of Nicol Bolas seems likely at either Mythic or Rare given that he is positioned as the key villain in the narrative at present, so we could end up with Nicol Bolas, Planeswalker in this slot or perhaps the original Nicol Bolas at rare
If you run out of cards in library just venture through Tomb of Annihilation to finish the job