Collision Dragon, Charging Pachycephalo

/:Engorge (When this unit attacks, you may retire one or more of your other rear-guards. If you do, it is engorged until end of turn) :If this unit is engorged, this unit gets +2000. : 1 When this unit is retired from for the effect or cost of your unit with "Gaia" in its card name, you may pay the cost. If you do, draw a card.