Barbflare Gremlin
The wrinkle is that this Gremlin taxes everyone at the table, itself included, and pays them for the privilege. Leave it tapped after a swing and every land anyone activates coughs up an extra mana of the same type, then singes its controller for one. Read the ability closely: it fires when a player taps a land for mana, so the trigger is agnostic to whose turn it is and whose land it is. During your own turn it doubles your ramp at the cost of a manageable trickle of self-damage; during everyone else's, it bleeds the table one point at a time for the crime of casting spells. That reframes it from a red beater into a symmetrical engine whose symmetry is the point: in a multiplayer game, three opponents tapping lands take three times the punishment you do, and the free mana they receive rarely offsets the accumulating burn. First strike and haste are there to make the creature stick and start pinging immediately, but the real design lever is the "if this creature is tapped" clause, which hands you the switch. Attack and the engine runs; hold it back and it does nothing. It is a Gremlin doing what Gremlins do best, breaking artifacts of the game's own economy, here turning the humble act of tapping a Forest or an Island into a slow toll booth.
