Futurist Sentinel
A 6/6 body for four mana is the kind of statline the color pie usually reserves for green, and the Vehicle chassis is how blue is allowed to borrow it. Crew 3 is the tax: the beater sits inert until you commit creatures to it, so the raw efficiency is gated behind a board you already have to be developing. That structure quietly solves a problem blue has always had with fatties, which is that a hard-cast 6/6 dies to the same removal as any other creature but costs you a full turn's worth of tempo. As a Vehicle, this one is an artifact when nothing is attacking, dodging sorcery-speed creature removal and sweepers between your turns, then becoming a threat only in the window where you can afford to tap down and swing. The math is deliberately clean: crew 3 means one three-power creature, or a pile of small bodies, flips the whole thing on, and the tapped crew are creatures you weren't going to attack with profitably against a 6/6 anyway. It reads as a plain curve-filler, and mostly it is one, but the design is doing the specific work of giving blue a resilient, hard-to-remove finisher without handing blue a genuine green beater outright.
