mewtwo pokemon card amazon V 030/078 - Go Weakness Psychic ×2 Retreat Cost Pokemon – Mewtwo – 150/165

Its not colorless and the colors of mana in its mana cost

Sunscourge Champion is fine with Panharmonicon but worse than it looks because generally you want to cast Sunscourge Champion on Turn 3, which happens to be the turn before Panharmonicon hits the battlefield

The other 99 cards must share your commander's color identity

The oracle text really helps here since it reads At the beginning of the end step, destroy all untapped creatures that didnt attack this turn, except for creatures that couldnt attack. If we look back at the Arbiter we see that there's no restriction on which creature can attack, so summoning sickness aside on my turn, it is likely that all but one of my creatures will get destroyed