Also odd that while Lancer and Rouxls can add themselves to your inventory as key items, Jevil and Spamton are both equippable, and it’s unclear whether they can revert to their animated forms from Jevilstail/Devilsknife and Dealmaker/puppetscarf respectively. Even the Spamton-shaped mannequin you can buy off an addison and take back to [Player]town is stored in equipment. I dunno if that’s something the Knight did to them or if that’s an aftereffect of shadow crystals on Darkners, but it’s… an interesting trend between hidden bosses.
What does it mean for beings whose Light World forms are already inanimate objects to become items/equipment in the Dark World too?
It is probably due to Shadow Crystals, since Shadow Mantle (which we presume to be Spade King’s mantle) seems to be conscious too, despite being an item.
The better question is, if this is a natural thing they can do normally, or is because they caught parts of Gaster.