March of the Machine Commander

Chant of Vitu-Ghazi

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Prevent all damage that would be dealt by creatures this turn. You gain life equal to the damage prevented this way.

Ravnica: City of Guilds

Convoke (Each creature you tap while playing this spell reduces its cost by {1} or by one mana of that creature's color.)
Prevent all damage that would be dealt by creatures this turn. You gain 1 life for each damage prevented this way.