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If you choose to cast any spells, you do so as part of the resolution of that ability

Is this also the work of Don Thousand

No, you cant use colorless mana for any color, as colorless mana can only pay for generic costs or specific colorless requirements

This is the case with Xyz in general, but since it is extremely strong against Rock, even non-Xyz mains would like to have some general-purpose EXs

It needs to be built specifically around and is typically quite slow to yield returns despite being so cheap to cast itself

This initial creativity helped spark a lot of notice for Lorcana and was a precursor of the nearly infinite unique ideas the Lorcana team is able to summon to support this incredible game