Wolf Mask

This is Halloween loot. Goodie Bags drop from enemies for the length of the seasonal window, and each one you open rolls a single costume item. The window follows your system date, so there is no in game trigger to hurry it along.

Since it is all tied to kill count, the best use of the window is a dense fight rather than exploration. Hoard the bags instead of opening them as they land, then run the pile in one go and trade the duplicates to whoever you play with.

A Moon Charm gives you the transformation on the game's schedule, at night and above ground, and takes it back at dawn. The mask hands you the head whenever you feel like it, underground or in daylight. Add the shirt and pants and the look is permanent, since social slots only touch appearance.