I've just bought a Mystical Donadak Plushie, but I'm confused on how to use it for a slot? Do I need to have A Gold account or something?

Um where did you buy it from? They no longer use those Plushies to give slots I'm sorry to say. You can buy slots with csc from the pets menu. You can get them with sp from the millionaire center. You can get them by picking the slot totem from loyalty boxes (you get them when you hit 2 years with the site). Or sometimes they are a prize from site events like a quest-a-thon. But no longer from Plushies.

Wow that's really annoying that I just spent 25 million on one plushie! Thanks for updating me though! :)

Ouch... Do you collect Plushies? It can go to that collection.

Otherwise try to sell it back to someone who does need it for theirs and use that sp to start buying from the MC slots. Just know they start at 20 mill and go up by 20mill per slot after up to 200 mill (10 slots all said and done) before it cycles again down to 20 mill.