We need a suitably sinister-looking bat cape, with maybe a wing-motif high collar.
Materials should be in the range of ~20 skins and ~10 wings, and of course some string and maybe a metal nugget for a teeny skull clasp. In addition to looking goddamn awesome, maybe it could bump Charisma and Stealth based on quality.
edit: This would be kind of silly, but maybe it would also act like bat-camouflage and prevent bats from attacking you, by making them think you're just their large, flightless, ugly brethren.