
The Applied Esoterica Badge is one of the more peculiar additions in PEAK, as the game doesn't describe what needs to be done.
If you're confused about what resurrecting your friend using 'unholy means' might mean, you're not alone. However, completing this badge is less complicated than you might think, even if it may take a fair amount of time to finish.
PEAK Applied Estoerica badge walkthrough
To obtain the Applied Esoterica badge, you'll need to play with at least one other player. You'll first have to let them collapse and die, since the Applied Esoterica badge has the resurrection requirement. If they're not dead, you can't resurrect them, can you?
You're also going to need the Book of Bones. This is a new Mythical item that has been added to PEAK as part of the Roots update. You can get it from the statue (they seem to be always present, but it could be based on luck. We will need further testing).

Once your friend has collapsed and they're dead, read the Book of Bones. This will revive them immediately, but not in the expected fashion. Your friend will be converted into a skeleton. They will have nothing but bones on them. You can read the Book of Bones by equipping it from the inventory and pressing the left mouse button.
This will complete the Applied Esoterica badge in PEAK. Do note that you'll have to let your friends collapse. Otherwise, you won't be able to use the Book of Bones on them. If you try to use it, it will be applied to yourself.
Using the Book of Bones on yourself will automatically convert you into a skeleton, but you won't be dead. In fact, you'll be immune to hunger and such needs, but taking even the minuscule fall damage will immediately kill you. The same rule applies if you use the Book of Bones on a solo run. Opening a cursed chest in skeleton form will also end your run, so be careful about when you want to use this item.
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