Versions

• Minecraft: 1.16.3

• Forge: forge-34.1.17

• Vampirism: Vampirism-1.16.3-1.6.0-beta.1

• ModPack: N/A

Issue Description

Crash when attempting to create a world

Reproduce Steps

launch pack and create world
it will go through the normal load process untill 100%
then when going to load world it crashes
Removing vampirism allows world to load normally

Additional Information

https://pastebin.com/b65wjxF1

Not sure why you closed it already, maybe you found a different workaround.
There was, at least a theoretical, bug in Vampirism here.