Colossal Plow

The trap is the crew number. Here is a two-mana Vehicle whose attack trigger produces three white mana and three life, but crewing it demands total power six, so the ritual it fuels is one you have already paid for by tapping down a board's worth of attackers. The mana that comes out is unusual in a way that matters: the persistence clause holds the across steps and phases within the turn, so it survives the combat and second main-phase boundaries that normally empty a mana pool. That turns the trigger from a Rite of Flame-style burst into something you can bank through combat and spend after damage, once you know what got through and what died. The design tension is entirely in the arithmetic: six power crewing a 6/3 that swings for six the first time, then hands you a ritual and a life pad on repeat. It wants a wide, expendable board to crew it and a mana sink big enough to justify draining that board every turn, which is a narrower ask than a colorless two-drop Vehicle looks like it should be. As a piece of construction it is a mana engine wearing a beater's stat line, and the crew six is the toll that stops the ritual from being free.