Stand As One

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.)
United Front deals damage to target opponent or creature equal to the number of creatures that convoked United Front.
Overload {7}{r}{w} (You may cast this spell for its
overload cost. If you do, change its text by replacing all instances of 'target' with 'each'.)