Minecraft, modloader and mod versions
Example:
Minecraft: 1.20.1
Fabric: Newest
Soulslike-Weaponry: 1.2.1

Describe the bug
After killing the day stalker the night prowler froze.

Add logs
A log of the incident, i.e crash log if a crash happened or a log giving other warnings before the issue occured if necessary.

Screenshots and videos

Other mods or relevant info
Neruina, but without that mod it crashes instead of freezing the boss.

Edit: Same thing happens to the day stalker if I kill the night prowler first

First off, I recommend using the newest mod version which is 1.2.1 instead of the outdated you are using (1.1.3).
Secondly, based on the short log you provided, it is likely caused by another mod's mixins. The Night Prowler is trying to remove all of it's effects from itself as soon as it enters phase 2 by calling a vanilla method in minecraft, so it is likely that another mod is interfering with this call and messing things up.

I would first try to update the mod to see if that helps.

Hey, I am using 1.2.1 I just forgot to change the GitHub issue preset. I added some more info on my other issue on the fallen icon.

crash-2025-04-03_11.21.59-server.txt

Here is an updated crash report using only soulsweapons and botania.

Ah I see, seems like the issue is the same as your other post about the Fallen Icon, gonna close this and follow up more there.