How to unlock Combat Slime (Lime): First, you must get to Stage 4-8 in the History chapter. To finish the quest to unlock him you need to bring 50 x Deadly Poisonous Jelly Jelly to him. When you start the stage, you go past the first area with monsters, and in the second one you see, on your map, a little line that goes down to the southeast. That is where you will find Lime. First you must kill the monsters around him to save him, then give him the 50 x Deadly Poisonous Jelly Jelly. After that you can go to the character creation screen and he will be available for play.
Go to south-east of Stage 4-8 (you must have 50 x Deadly Poisonous Jelly Jelly in inventory}
Kill monsters around damaged slime (it's very easy)
From now you can use Combat Slime (Lime) character
Deadly Poisonous Jelly Jelly:
monsters: Jungle Slime, Deadly Poisonous Jungle Slime
stages: Stage 4-1, Stage 4-2, Stage 4-3, Stage 4-5 - recommended