Haakon, Stromgald Scourge + Morophon, the Boundless + Nameless Inversion + Cloud Key

Prerequisites

• "Instant" chosen with Cloud Key.

Steps

1. 1Cast Nameless Inversion from your graveyard, as it is a Knight card, by paying due to Cloud Key and Morophon, giving a creature +3/-3 until end of turn.
2. 2If the creature has toughness 0 or less, the creature dies as a state-based action.
3. 3Repeat as desired.

Effects

• Reduce the toughness of creatures opponents control to 0
• Reduce the toughness of each creature opponents control to 0 upon entering