A card that both supports multiple themes and progresses the game while also creating competition, not by being wanted in more then one deck, but instead by making two existing decks want the same cards, is a work of true design beauty
Dramatic Reversal + Isochron Scepter is an easy one (infinite mana + draw)
This can inform our land count
You can feel safe with just a poxy Mentor in play when you pass, have them cast two or more things at end of turn, untap and cast a bunch more non-creatures and just kill you
For example, this means that normally, if you control Hunting Velociraptor, you can cast Grim Giganotosaurus for its prowl cost only if a Dinosaur dealt combat damage to a player, but if an effect causes the spell to have other creature types, the prowl ability is also satisfied by a creature with those additional types having dealt combat damage to a player