This seems really hard to use. How are you going to be putting creatures onto the battlefield before this? Preparations and creatures with Preparation will do the job, but you often won't have many of them in your deck or hand. At that point you'll generally have to cast a 2-drop or 3-drop creature, at which point this is coming out as a 3/3 or 6/6 on turn 5 or 6, which is not how mythics should play.