polymorph cards mtg True Foil - AFR Maybe a little *too* convincing. Codex Card Database | Polymorph:

That player may pay 10 life

While great together, first strike and haste don't overlap much, and on Master Piandao the ability makes it more likely Piandao will survive the attack, and on Glorybringer, haste ensured you can attack and exert it right away

Its easy to make this a big flier that drew you 3-4 cards over the course of a few turns

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Mutated Cultist's second ability)

Its also potentially good later on in some games too, because some creatures have a high power but low toughness or vice versa