Titania Character Stickers by Barry Bradfield Minimates it is the "Bullet Factory"

it is the "Bullet Factory" from Brick Warriors

You could do this with several different gray hair pieces

The third set of Teenage Mutant Ninja Turtles Minimates joins the two previous sets

Hair - Marvel W81 Phoenix (but you may find others that work well)

Titania Character Stickers by Barry Bradfield Minimates it is the "Bullet Factory"This is a set of character stickers for Titania, created by legendary Minimate designer Barry Bradfield. They are printed in high resolution by our printing partner, 8 Bit Hero. They are also pre cut, so they are peel and stick. I do recommend running a black sharpie around any dark stickers after peeling but before applying. Here are the recommended parts for this custom: Hair Marvel W81 Phoenix (but you may find others that work well) Body Base