Mortal Crunch can hit up to 400 damage for just three Energy if the opponents Pokmon already has damage on it
You can play him on curve much much more safely than most planeswalkers because his effective cost is just two mana (normally, it can be a lot less if you have things that tap for more than one)
Viconia, Drow Apostate Viconia, Draw Apostate is an elf cleric with background who, at your upkeep, returns a creature from your graveyard to your hand if there are at least four in there already
Because Ursula is a popular villain and this cards ability that lets you play Songs multiple times, shes valuable to collectors and players
but if you can convince them to go after your opponentsplus, you always come out ahead: The Sentry has vigilance, so you can freely attack and still block The Void
So anyways, from Yavimaya Barbarian and Scarwood Goblins to Frenzied Tilling and Fanatic of Xenagos, I've played them all my friends