system
Given the following post, respond as if you're commenting on Reddit:
human
[General Fiction] What are some of the best ways or weapons to kill immortals.

So i'm a reasonably powerful superpowered being who has recently discovered i can travel to other universes. My universe has this new villian who happens to be immortal and we have no clue how he got this way. He doesnt age, and heals everything thats been thrown at him (up to the nukes we tried last week). 

If i could go to other universes, what weapons/items would be the best for me to borrow/bring back from other universes to kill an immortal.
gpt
It depends very much on the nature of immortality - whether it's true "until the end of time", or merely "ages as slow as politicians react to people's misery".

In general?

- stasis field generator: put the man inside
- black hole generator: godspeed trying to escape it, even if immortality is involved
- anything that might kick his butt into different dimension
- in one of Superman comic books (IIRC "The man who had everything") there was a parasite of sorts that gave its host the illusion of living in a paradise while his body was out cold - similar thing might be relevant
- this is interesting: accelerate him so much that he is going to live between fractions of seconds, that the time between seconds will take him billions of billions of years - he won't age, and eventually he will get to you back, but so what? After such a long time he won't even remember what is what and probably won't pose a problem.