Wow, he casts Overrun each turn? I fear this may need to be rare as well (cf Kamahl, Fist of Krosa).

kamahl's a wimp. j/k maybe commons and uncommons don't have activated abilities, just the trigger. rares have both trigger and activated.

That's a sensible plan. I do like how clever this cycle is... but I get the impression that it reads better than it plays. Too often, players will forget they're supposed to add Trample to their 3/3s when they play a Scaled Wurm. Players are bound to shorthand the two abilities into "Pay 5: Creatures gain +2/+2 and trample." A batch of uncommons to 'train' players to trigger the abilities the right way will make the rares more relevant.