Cogwork CubeCogwork Assembler Buy + Doubling Cube Buy
It's not good, but it does work. Mostly intended for EDH.
Start with 14 mana of any combination of colors and both in play. Tap Cube (14-3=11, x2=22 mana). Activate Assembler targeting the Cube (22-7=15 mana left).
Net infinite mana of any combination of colors you started with in your pool. It's technically a colorless combo, so it fits into any deck.
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