After both his son, Asriel, and adoptive child, Chara, died in one day, Asgore became devastated. He lost his mind and held an even stronger grudge against humanity. Before the death of his two children, his personality was actually more similar to his Undertale counterpart, kind, fatherly and caring. Now, after the death of his children, he declared a new rule, and the motto of the monsters:
Kill or Be Killed.
Asgore in Underfell has black hair and a beard, yellow scleroses with red pupils for his narrow devilish eyes, and a red cape with golden pauldrons that cover his dangerous armor. His horns are identical to that of a bull's, except instead of being curly, his horns are pointed up. Like his counterpart, his fur is white, but he has longer fangs. His weapon may be a flaming spiked meat cleaver, but this is not agreed upon across most versions. He is also a little taller than his Undertale counterpart.
Like most characters in Underfell, Asgore has a strong, negative personality compared to how he was in Undertale. He has an ultimate urge to kill humans. He was always known as a harsh king, especially after Toriel left him when he forced the 'Kill or Be Killed' rule onto everyone. He threatened to personally hunt down anyone who disobeyed him, so that every monster had to gain LV quickly to survive. It was at that time Asgore became much more cruel.
Powers and Abilities
King Asgore has almost the same abilities as his Undertale counterpart. He uses his weapon with a blue and orange attack. He can also manipulate flames like Toriel. His attacks cause more damage and are slightly quicker in speed.
This fight is very similar to the Undertale fight. However, after a few words, Frisk immediately enters battle with Asgore in the Throne Hall. After the fight, on a Pacifist Route it is true that Frisk would save Asgore. Asgore is surprised as everyone on the way tried to kill Frisk. In the Timeline of Genocide, Frisk immediately kills Asgore, initiating the Alpha Flowey fight.
Toriel: Toriel is Asgore's ex-wife who lives in the Ruins.
Chara: Chara was the adopted child of Asgore and Toriel before dying of a bee pollen overdose.
Flowey/Asriel: Flowey/Asriel is Asgore's son, but Flowey is terrified of him. Asgore doesn't actually know that Flowey is his son.Frisk: Asgore tries to kill Frisk, but will eventually be killed by either Frisk or Sans.