Inominox

You fight it in Peak Tyrant.

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.

Winning it gives ×5 EXP and ×5 coins.

Its data gives its Nexomon HP ×1.45 and stamina ×1.45, but this build never applies that: the game only uses these modifiers behind a switch it leaves off.

What its boss cores do:

• A boss vitality core (75): 75% more max HP.
• A boss stamina core (300): 300% more max stamina.