Continuation of Season 3, The Manequin is fighting Gaster in middle of void realm, trying to gain power or rather kill gaster.

Meanwhile in Mt.Ebott

The Underground got bored, and therefore, Asgore decided to high up some stakes, an Underground fight in the cage.

Anybody who survives gets the title of the bravest human/monster alive.

but those who loses. gets to be claimed in title of "weak"

Asgore proposes 2 v 2 situation.

Toriel tries to put penalties to avoid death or more likely severe Injury to either human or a monster.

Frisk despite being pacifist has to be involved in the combat.
Papyrus becomes Frisk's coach, teaching them how to self-defense in case things go south.

and sans teaches frisk how to remain calm and keep themselves on guard and locked in.

And so Season 4 Begins as Asgore says "May the best Suvivor win."

and so the brawl in cages begin.