As a land, Urzas Saga can be played for no mana and functions as a colorless mana source for the first two turns
Speaking of lands, another honorable mention are the MDFC land cards from MH3 in general
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It doesnt trigger multiple times if you cast a spell that targets a creature you control multiple times or that targets multiple creatures you control
Its not too exciting, but if youre just buying a stack and then buylisting them, its easy money
I cant do combat damage at all