Going for 100% Research Completion; What Items Should I Look Out For?

Basically the title. Which items are going to be the hardest to obtain for full research? I have a few of the rare banners; Tim, Rune Wizard, Nymph, Crawdad+Salamander+Shelly (PLEASE do this in prehardmode if you don't want it to take hours, they were twice as rare as nymphs). The Cultist banners are probably gonna be a grind but ultimately not dreadful. I'm gonna need to create a second character to get the torch god music box because I'm pretty sure I did it already.

I thankfully have a fair few of the travelling merchant's items, including the halo and sergeant united shield.

The only thing I dread trying to obtain is the bone key. I've never fought a dungeon guardian before and I'm not gonna just cheese it with godmode.