So...I defeated a Nightfall Mender, and after winning the battle, I supposedly won a Design: Nightfall Mender's Cavalier Hat. Yep...pretty sure I saw the name right. I know that both the Design and Mender's bit were in the dropped item name.

Afterwards, I went to check my inventory and...no new item, period. Unfortunately, I didn't get a screenshot because I kind of didn't expect a glitch or whatever.

Regardless, I think it was supposed to be either a Mender's Hat or the recolorable design, but I didn't receive either.

Did you check the Blacksmith part of the Barracks?

One of the crafting tabs within the Blacksmith is for Avatar Items, so when you acquire a crafting pattern it goes to the list there rather than being an inventory item.

If you don't have the Blacksmith part of the Barracks unlocked yet, I'm pretty sure the item will just be sitting there until you can access it.

Oh, OK...no, I don't have the Blacksmith unlocked yet...all I have so far is the healer and the item shop.

Yeah the avi drops from the lost grove are just patterns you have to forge yourself (with the exception of the extremely rare held drops that Malfy and a few others drop)