Bladed Sentinel

A 2/4 body wants to block, and the activated ability admits it: the only way this construct ever does double duty is by paying white mana to keep watch after it swings. That is the whole bargain. The 2 power means attacking accomplishes little on its own, so the design steers the card toward defense first, then lets a white deck convert the body into a soft, repeatable attacker that still holds the ground behind it. The cost structure is the giveaway about which color was meant to find it: a colorless artifact creature that anyone can cast, but whose payoff is gated behind a white pip, a piece of filler tuned to reward a deck already committed to white without locking out everyone else. There is nothing here for a combo player or a Constructed grinder; it is a defensive role-player for an aggressive-leaning white shell that needs a wall it can occasionally point at the opponent. The vigilance grant is not free and not permanent, which keeps the rate honest: each turn you want both jobs out of it, you spend again.