Oblivion Stone, Nevinyrral's Disk, Perilous Vaults Resource denial
Plot lets you prepay for a spell and cast it from exile on a later turn
Jwari Disruption and Sink into Stupor serve double duty as both interaction and lands
Even if one isn't playing those colors or doesn't have Channel-Fireball, a Black Lotus can give a nice mana bonus for a player, allowing them to play powerful cards in the early game
So small margins probably work because they are often something that is liquid and pretty repeatable
Green Goblin doesnt just discount his Mayhem cards either, but every single card you cast from the graveyard, which not only makes it far better in Commander, but allows the card to see potential play in constructed, as well