Buyback is the greatest thing ever to happen to Magic.
Without Buyback the game has been a shadow of it`s former self, and I blame the loss of Buyback for the poor state of tourney Magic at the moment. Buyback succesfully rewrote the fundamental of Magic strategy - card advantage - and transformed the game for two years. I`m not certain that it was properly exploited however - I would like to see it come back in another set with some new effects.
Erik, I do hope you aren`t serious about Buyback being broken. There were only ever 3 good Buyback spells (Whispers, Forbid, Capsize) and one funky one (Corpse Dance). The best Buyback spell wasn`t even a Buyback spell (Recurring Nightmare). Good? yes. Broken? no.
Slivers were interesting, but only because of Crystalline were they playable. ACC nice, but like Buyback the ability was so good they couldn`t afford to make too many good ones (FoWill, Contagion, Misdirection, Unmask).
Spiderman is the only person to get the right one.
By far the best mechanic, and the only one that has perservered beyond the set in which it debuted, is 'Coming Into Play Abilities'. Nekrataal, ManOWar, Uktabi Perverts, Ravenous Rats, Avalanche Riders, Ghitu Slingers, Wall Of Blossoms, Yavimaya Granger...
I vote for 187!