MTG Keyword Rules — Comprehensive Rules Glossary

Fuse is a static ability found on some split cards (see rule 709, “Split Cards”) that applies while the card with fuse is in a player’s hand. If a player casts a split card with fuse from their hand, the player may choose to cast both halves of that split card rather than choose one half. This choice is made before putting the split card with fuse onto the stack. The resulting spell is a fused split spell.

A fused split spell has the combined characteristics of its two halves. (See rule 709.4.)

The total cost of a fused split spell includes the mana cost of each half.

As a fused split spell resolves, the controller of the spell follows the instructions of the left half and then follows the instructions of the right half.