Folicurse

You fight it in Dark Woods East, during Citadel Under Attack.

Its Nexomon's levels are rolled when the battle starts, from the story's difficulty, as the Battles page explains.

It's a wild battle, but it doesn't allow capturing, so the capture option never shows. Its Nexomon's levels are hidden during the battle.

Winning it gives ×2.5 EXP and ×2.5 coins.

What its boss cores do:

• A boss vitality core (150): 150% more max HP.