Lightless Evangel (Uncommon) Grows stronger each time you sacrifice a creature
And yes, I hear your shouts of Buy it on eBay!, but its not about that specific card
For those who don't mind digging back into the archives, there's another option, maybe the best one, that's been there since almost the very start
Barbarians Between Conan the Barbarian and Dungeons & Dragons, the Barbarian is a fantasy-flavor home run, and as a typal strategy it's fun to build a deck around a "profession" rather than a species
In addition to the obvious things like Syphon cards (do some effect to each other player, gain benefits depending on how many other players this hit), there are cards that affect a random opponent, cards that give everyone the game the ability to join forces to create a big effect (for example, a sorcery that lets everyone pitch in mana and then lets everyone put lands into play from their decks), and Enchant Creature cards sorry Auras that boost the creature while preventing it from attacking to