pikachu jumbo pokemon card - Oversize/Jumbo - SWSH061 Pikachu does 10 damage to itself. Pikachu V SWSH198 - Jumbo

Similarly, Oldschool 93/94 + Artifacts = Robots

Galvanic Iteration Galvanic Iteration allows you to copy other instants and sorceries for cheap, for 2 mana first and 3 later

If its your turn, you can nab the best board for the turn and do some real damage

Honorable Mentions The Odyssey Eggs The original Odyssey Eggs dont fit my description of giving you a card back, although they fit colorless mana into specific colored mana like the signets

And a creature-centric G/R Ramp deck With Cinder Glade really wanting a very low non-basic count (including themselves), I chose to go very lightly on them, with just two and a lone Rogues Passage

If youre one of the lucky few who possess one of these cards in your collection, congratulations