Hylda of the Icy Crown + Opposition + Phyrexian Altar

Hylda of the Icy Crown

Opposition

Phyrexian Altar

How it works

1. Activate Opposition by tapping an untapped creature you control, tapping a creature an opponent controls.
2. Hylda of the Icy Crown triggers, holding priority, activate Phyrexian Altar by sacrificing the creature tapped in step 1, adding 1.
3. Resolve the Hylda of the Icy Crown trigger, causing you to pay 1 to create a 4/4 Elemental creature token.
4. Repeat.
5. You may also repeat this loop during each turn.

This engine locks down the entire board by turning your own creatures into versatile disruption through Opposition, allowing you to tap down an opponent's creature on demand. Because Hylda of the Icy Crown watches for you to tap an opponent's creature, each activation triggers her ability to reward you with a payoff for just one mana—which is conveniently provided right on time when you use Phyrexian Altar to sacrifice the creature you just used to tap down the board. That sacrifice feeds the Altar to fund Hylda's triggered ability, generating a fresh 4/4 Elemental token to replace your sacrifice and keep the loop spinning indefinitely.