Adventuring Party

Convoke (Each creature you tap while casting this
spell pays for or one mana of that
creature's color.)
As Adventuring Party enters the battlefield, you
may discard any number of
cards. Adventuring Party costs {w},{u},{b},{r}, or {g} less for every 2 cards you discarded.
Creatures you control gain +1/+1 for every creature
you control.