Seeing their best card go to their graveyard is a big morale blow
The Dina, Essence Brewer Commander does have the ability to do this, but it costs two mana and requires her to be tapped, which can be costly for a single sacrifice, even if it does activate other effects
This, and the fact they often feature gorgeous art of fan-favorite Pokmon, makes them extremely coveted
Greninja's usual blue (or black when shiny) color palette is fairly muted, perfect for a stealthy frog, but this rainbow recolor ruins any chance of a quiet entrance for this ninja
Overall i think this archetype could not have a deck built around itself
Its good on defense, it filters your draws while youre setting up, and it turns into three extra cards when you dont need it anymore