You can get black pearls from squids and lobster things in the ocean.
Use before killing lots of baby gigas lots of xp
Use to tame the rainbow centipede in caves and on scorched earth
Use it before completing swamp or yeti cave for extra xp
Use it before birthing/taming a reaper
Use on reaper Queens when you get the embryo
Use it before trophy room pursuit(mobile only)
Unsure if this works and currently no way to test it but take a dump at a toilet eat this and finds a 4x explorer note for most exp ever?
for taming an arthropluera this is the item you need to craft since it likes only take 1 at any level (if your on mobile it takes 1 for 300 and 450 for hard and brutal difficulty players)