Volcel

You fight it in Cook Field Boss.

Its Nexomon's levels are rolled when the battle starts, from the story's difficulty plus this battle's own weight of 3, 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 (600): 600% more max HP.
• A boss stamina core (500): 500% more max stamina.
• A boss immunity core (70): 70 off the chance of every ailment against it.