They have most of the same common cards, but the real difference is the special full arts
In practical terms, this means your Pokmon can use any attack regardless of what Energy you have attached to them a flexibility that can catch opponents completely off-guard
A Clone for four is a little behind, but not that much

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Oonas Grace had to cost three mana because a two mana version would grant every land Cycling, but one can imagine an Escape cantrip that costs one mana, but whose Escape costs an exorbitant six cards or four mana (but not both)