Perpetual effect seem to protect creatures from getting destroyed. To reproduce : Play brawl. 1. Have a player play the "seek a card/hardened scale" enchantement. Have him play bristy bill. Have him seek bird of paradise winding constrictor. have him play bird of paradise, have him play winding constrictor. Have the opponent play "the returne one creature to your hand, then boardwipe" spell. Bird of paraides and winding constrictor have their perpetual effect removed but otherwise stay on the battlefield.