https://www.curseforge.com/minecraft/mc-mods/respawnable-pets

Seems to work with other modded mobs, but not with the chameleons, mystery egg creepers or baby spiders from Primitive Mobs. It'd be nice if they worked together. Unfortunately, the other mod doesn't have an issue tracker, or I'd report it to them too.

Edit: they have a link to the issue tracker now

Edit: it seems it works with the treasure slime, just not any of the others.

Made this work for the next update for what it's worth xD a year old post