Blood Funnel + Corpse Dance + Witch Engine

Blood Funnel

Corpse Dance

Witch Engine

How it works

1. Activate Witch Engine by tapping it.
2. Holding priority, cast Corpse Dance with buyback by paying 2 due to Blood Funnel.
3. Blood Funnel triggers, causing you to sacrifice Witch Engine.
4. Resolve Corpse Dance, returning Witch Engine from your graveyard to the battlefield, giving it haste, and returning Corpse Dance to your hand.
5. Resolve the Witch Engine ability from step 1, adding and failing to give an opponent control of Witch Engine as it is a new object.
6. Repeat.

This clever loop turns Witch Engine into a self-sustaining mana engine by leaning heavily on Corpse Dance's buyback mechanic and instant-speed flexibility. When you tap the Engine for four black mana, its delayed drawback of handing it over to an opponent is completely circumvented because Blood Funnel conveniently forces you to sacrifice the creature as a tax for casting Corpse Dance. That sacrifice sends the Engine straight to your graveyard, primed and ready to be brought right back to the battlefield with haste by the very same Corpse Dance resolving back into your hand.