Key and Mori suggestion
I play both sides of the game, and we already know it but Keys and Moris are way too strong.
In addition to the suggestions below, my recommendation is to also increase the cost for obtaining both with Bloodpoints. Something like 20k-30k would be a good start. I know that doesn't alleviate those who have already stockpiled on them, which is where the second part of my suggestion comes in
Key suggestion:
Instead of opening a hatch instantly, there needs to be a cast time just like opening gates. It doesn't have to be as long but it can synergize with perks like Remember Me so that way if you see a group is bringing a key, you can switch out perks (similar to Franklin's Demise) to be prepare for the item. The cast time could be short, maybe 15-30 second range. That way if the killer spots the hatch, they can at least keep an eye on it and not lose instantly and dePIP just because of a very strong addon. I would also say adding skill checks (which could also synergize with some killer perks) to potentially speed up the hatch opening process. This rewards good players. In the end, Keys will be a little more balanced, and it's not an instant loss. Otherwise, killers have to slug and prevent any more deaths to prevent hatch from spawning.
Mori suggestion:
This one has been suggested a lot, and it's honestly a no brainer. Some respectful killers already do this. But Mori's should only be unlocked once the survivor has been hooked twice, or they've went in to struggle from their first hook. Basically, the survivor needs to be dead the next time you would hook them. This would balance it a bit more, and give survivors at least a fighting chance when an Ebony mori is brought into the game.
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Some will say to just remove both, but I just don't see that being done, so at least balance them better please. I'm open to more suggestions, but these are the 2 I think would at least make the item/offering more balanced and bearable.