Tenth Edition

Avatar of Might

If an opponent controls at least four more creatures than you, Avatar of Might costs {6} less to play.
Trample

If an opponent controls at least four more creatures than you, this spell costs {6} less to cast.
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)

In their most desperate hour, the elves of Llanowar had one song left to sing.

Prophecy

Trample
If an opponent controls at least four more creatures than you, Avatar of Might costs o6 less to play.