Hi I was testing mods for my modpack and I found out that BP and Mystcraft if they are together and travel to a mystcraft dimension it crash (I test it with only mystcraft and bp)
Heres the crash report:
https://pastebin.com/T3bednSV

That doesn't really look related to BP, it's somewhere in Mystcraft's world generation code. Try reporting it on the Mystcraft tracker, maybe they can tell what's going on.
Also give BP 0.3.x a try, lots of stuff has changed.

Ok thank I will check 0.3.x and if still crash I'll report it in mystcraft thanks

Can confirm that BP 0.3.4 is still causing a mysterious crash with Mystcraft:
https://paste.dimdev.org/urixofaxus.mccrash

According to the crashlog, it would appear to be something related to mob spawning parameters?
Chunks begin to load on the client before crashing, so it's not related to worldgen.

However, because Mystcraft isn't open-source, it's hard to know whether this is an issue with Mystcraft's implementation or BP's.