Which spells/potions/etc have Eliezer declared too overpowered to appear in HPMoR, or at least nerfed considerably?

Context: Ten years ago, when I and my writing allies were considerably more stupid, we started on an RPG that wound up fitting the insane crossover tropes a bit too closely (Sauron and Jedi have yet to show up, at least...). It's still ongoing, if considerably slower due to everyone else getting lives, but as some tenth aniversory shenanigans, we've started rewriting the first couple years to not suck, and I've realized that I really need to pay more attention to Harry Potter magic for it to make any sense, even though I kept the HP references as few as possible. So far, I've already made use of Voldemort's horcrux cave from Halfblood Prince, and am going to look up exactly how the fidelius works next.