system
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human
[Harry Potter] Is there an upper limit for how powerful of a being that an avada kedavra spell can kill?

Is avada kedavra an automatic death for *anything* that it hits? Could it kill a blue whale? Pando, that forest of thousands of trees that are actually all one tree? Could it one-shot Ego, the living planet? And would all of those require the same amount of energy, or would it take more effort to kill a larger being?
gpt
>Is there an upper limit for how powerful of a being that an avada kedavra spell can kill? 

Definitely. It's impossible for us to say where exactly those limits are, but the curse has failed to kill twice that we know of. (after being cast and landing successfully) In both cases, it was a pure (HP)magic vs (HP)magic situation. Once we cross into other universes, things become even more speculative. 

>would all of those require the same amount of energy, or would it take more effort to kill a larger being? 

"Power level" is a binary here; You're other strong/willful enough to cast the curse, or you aren't. That's part of the reason that the curse is considered so dangerous. If you successfully cast it on me, I'd be just as dead as if Voldemort had done it.