Restful Buckling

Creatures cast by maturing Restful Buckling have trample and haste.
Whenever you discard a card, you may mature Restful Buckling.
(To mature Restful Buckling, exile it. If you do, search your library for a non-Young creature card that shares a creature type with it. You may cast it by paying the difference in mana costs between it and this creature. Then shuffle your library.)