-1/-1 tokens. Take advantage of creatures that enjoy having -1/-1 counters put on them.

Self-sacrifice. Mostly black. Play creatures that keep coming back from the graveyard, and enable powerful effects when there is sacrificing.

Blue-green with Auras. Can't be targeted by opponent. Inspired by Dave's deck.

Cycling + Retrace. Gain huge advantage with cycling and discard effects. Related: Red-Blue spells matter deck.

Blink. Classic advantage.

Zombie aggro. Mono black.

Artifacts. Cards that reduce costs, and throw artifacts on the battlefield.

Dredge. Also Landfall. Graveyard shenanigans.

Allies. White Black, mostly, for fun life gain