Emergent Woodwurm [March of the Machine Commander]

Backup 3 (When this creature enters the battlefield, put three +1/+1 counter on target creature. If that's another creature, it gains the following ability until end of turn.)

Whenever this creature attacks, look at the top X cards of your library, where X is its power. You may put a permanent card with mana value X or less from among them onto the battlefield. Put the rest on the bottom of your library in a random order.