Chippy's Helmet

The whole outfit comes off one particular version of Skeletron, the red hat variant. Beat that one and every piece drops together, so there is no chasing a missing greave afterward. Beat the ordinary version and you get none of it. Either the fight hands you the set or it does not.

Chippy's Cloak (Inactive) arrives alongside the clothes and is the one piece that is not just a costume. It has to be crafted into its working form before it does anything, so do not file it away with the vanity when it lands.

Four cosmetic pieces, and the headband behaves differently from the rest. Slot Chippy's Headband into an accessory space and it streams out behind you once you are moving quickly, but only while your hair is on display. The full set does that, a Familiar Wig does that, and so does any head slot left empty. Cover the hair with a normal helmet and the trail stops.

Chippy was given one pick for something to put in the game, and this is what he spent it on.