Its required commitment to white means that it would be at its best in the heavy-white decks that already have strong options at two mana in Luminarch Aspirant, Intrepid Adversary, and Thalia, Guardian of Thraben
5 The Seventh Doctor And Ace, Fearless Rebel A Heady Mix Of Chaos And Carnage The Seventh Doctors quirky, volatile nature comes across perfectly in his ability, which lets you play mind games with an opponent with a free spell on the line
The reason that matters is because Genetic Apex came with 266 cards to collect (along with secret rares on top of that) divided up over the three separate pack types (Charizard, Mewtwo, and Pikachu)
If Valley Mightcaller enters at the same time as one or more other Frogs, Rabbits, Raccoons, or Squirrels you control, its second ability will trigger for each of them