+Duo (8)
Whenever you cast a black spell, Emberstrike Duo gets +1/+1 until end of turn.
Whenever you cast a red spell, Emberstrike Duo gains first strike until end of turn.
First strike
If a source would deal damage to an opponent, it deals double that damage to that player instead.
Whenever you cast a blue spell, Gravelgill Duo gets +1/+1 until end of turn.
Whenever you cast a black spell, Gravelgill Duo gains fear until end of turn. (It can't be blocked except by artifact creatures and/or black creatures.)
Whenever Marching Duodrone attacks, each player creates a Treasure token. (It's an artifact with ", Sacrifice this artifact: Add one mana of any color.")
Whenever you cast a green spell, Safehold Duo gets +1/+1 until end of turn.
Whenever you cast a white spell, Safehold Duo gains vigilance until end of turn.
Assist (Another player can pay up to of this spell's cost.)
When Spellweaver Duo enters the battlefield, you may return target tapped creature to its owner's hand.
Whenever you cast a red spell, Tattermunge Duo gets +1/+1 until end of turn.
Whenever you cast a green spell, Tattermunge Duo gains forestwalk until end of turn. (It can't be blocked as long as defending player controls a Forest.)
Whenever you cast a white spell, Thistledown Duo gets +1/+1 until end of turn.
Whenever you cast a blue spell, Thistledown Duo gains flying until end of turn.
Gatherer works better in the Companion app!