Best friends with Acererak the Archlich: If you can find a way to make that extra mana for free you can just keep looping it and win the game unless your opponents can do anything about it
By using cantrip and draw effects as well as mana generation cards like Dark Ritual, Black Lotus, and others, it's easy to instantly kill a player without them ever having had a turn
Sephiroth, the Savior (Atraxa, Grand Unifier) This one I'm surprised at as well, but because of how low it is
If so, Cenote Scout will almost certainly be a huge part of the deck
Once each turn, you may cast a spell from the top of your library if it shares a card type with a card exiled with this creature
Isamaru can make a formidable Voltron deck as well, with its low cost for a 2/2, throwing great equipment and auras at it can quickly overwhelm your opponents if they can't deal with it quickly, or let it sit thinking it's not that big of a threat