If you look closely at the left side of the frame, you can see the exact moment that young Timmy Tibble’s soul is sucked out and replaced with a demon.
not really, sorry! this is a really specific strange question
edit: ah yes according to people you might be thinking of one of my favourite characters, mrs. bofeeni but she wasn’t a moose. however, a moose named mr elken in the same episode is what you were describing, it’s all in Arthur’s Substitute Teacher Trouble!!
dont know how its spelt but its mrs. schmagaiey (smth like that) but did not quite have white hair yet