The Transform Card series
While I still think differently-colored activation costs are the secret tech that would make a 4-colored color-identity legend work the best, Innistrad block introduced some new tech — double-faced cards — that provide another option. Again, you only need 2-colors to cast it, but they’re better with 4.
Some of these cards are my favorites, and a few need a bit more work.
Torkin was partially inspired by Huntmaster of the Fells, and partially by Pikel Bouldershoulder (from R.A. Salvatore’s Cleric Quintet). He’s a lord for the birds and the bears (that he makes), but he can switch back and forth depending on what you need defensively.
Daikatimor is a Rage Demon. He’s a pretty brutal beater, and a potential 2-turn clock. However, his transform condition (which I think might need to cost more), curses him into becoming an innocent young girl (just waiting for blood to be spilled to reawaken the Demon within), who also makes your team into great blockers (if pacifists).
Dialda, of the Doesn’t-have-a-cool-title
Dialda is a Knight who has studied tactical strategy, but she has some anger issues. I wonder if the Double Strike side with the slith effect might be too attractive/powerful. I also think I’d use a less optional transform cost.
Gwynne, Handmaiden of Trest
Sure, Edric does the spying bit, but silly little court-maiden Gwynne does the dirty work. First she disarms you with her charm (and convinces you to give her gifts), but if you get in her way, or if you just need killing, she will eliminate you and then disappear in to the mists, leaving people none-the-wiser.
I have a rule against Time-Travel… it’s confusing, and rarely done well. The baddass Mad Scientist speeds up time for you by giving you more cards… glimpses into the future… but if you pay the cost you get accidental rampaging dinosaur that eats time (preventing you from drawing cards, and requiring a sacrifice of hand), but also buys you time (more attack phases).