The lime slime is now a follower and you can recruit them from the lich dungeon. Befriend them by giving them a growth potion in the dungeon and they'll meet you outside.
I only found a green slime asking me for potion. Others will attack me.
Besides, there was a white lizard outside the crystal dungeon after I beaten rank 20. It is a new follower, cannot grow by leveling, and I still don't know how to grow it...
