I like the idea of turning a mana rock into a creature after I've already used it for mana, but I'm sure you can come up with something more devious
It also digs in a 100-card deck and puts stuff into the graveyard for recursion, so it's synergistic with the format and various archetypes like Golgari Reanimation
You can absolutely spend 45 minutes agonizing over a frame choice for a card that taps for one mana
A very Nito thing I was able to work on
Annihilator comes with a number (for example, annihilator 2), and when the creature with annihilator attacks, the defending player must sacrifice a number of permanents equal to the number associated with annihilator
The rest of the field added discard, counters, or Elesh Norn, Mother of Machines to stop the battle