The Power Of Friendship

Target creature gets +1/+1 for each other
creature you control until end of turn.
If you cast it using flashback, put that many
+1/+1 counters on target creature instead, then
if ten or more counters were put on it this way,
win the game.
Flashback {5}{g}{w} (You may cast this spell from your graveyard for it's flashback cost, then exile it.)