Asgore forces the protagonist to fight him, and the protagonist cannot spare Asgore. The protagonist's HP can never drop below one on any given turn; this gives them a chance to heal every time that they reach 1 HP.
During the battle, Asgore uses attack patterns similar to Toriel's. He also uses light blue and orange attacks in which the protagonist can see the upcoming attack pattern by looking at Asgore's eyes, which flash the attack color pattern.
After dealing the final blow to Asgore, the protagonist can choose to either "FIGHT" or give him "MERCY"; the "MERCY" button has cracks in it from being shattered.
- Note: All damages assume no armor and LV 1.
Asgore's attacks are faster and more intense versions of Toriel's attacks. The assault ends if the protagonist reaches 1 HP and does not have 1 HP already.
- Several waves of small fireballs from the top of the screen, which move in curving patterns. This attack does 8 damage per hit.
- Smaller waves of small fireballs (6 damage per hit) move down the middle of the screen are interspersed with massive clouds of projectiles that cover entire sides of the screen (8 damage per hit).
- Partial circles of fireballs that gradually spiral in around the Bullet Board. This attack does 8 damage per hit.
- His hands move along the sides of the screen, leaving behind large fireballs that move towards the protagonist's SOUL after all the bullets appear. They home in on the spot where the SOUL was when they began moving. This attack does 6 damage per hit, but the paws do no damage.
- Rings of large fireballs fire from the top of the screen, gradually moving from one corner to the other. This attack does 6 damage per hit
- Asgore's eyes flash blue and orange randomly, followed by sweeping strikes in the same order of the flashes of his trident, which hit the entire Bullet Board. This uses blue and orange attacks. This attack does 6 damage per hit.
With no MERCY button, the protagonist has no choice but to attack Asgore until he reaches a sliver of health. They may then spare or kill him.
Asgore's attack and defense can be lowered in two ways:
- Consuming Toriel's Butterscotch Pie during the boss fight, which reminds Asgore of her.
- Talking to Asgore three times. (Only if the player has not killed anyone)
His attacks end if the protagonist reaches 1 HP and begins at a higher amount.
Asgore's attacks become faster as the battle goes on, but none of them can kill the protagonist unless they are already at 1 HP (so damages greater than the current amount of HP does not zero it out). Otherwise, the protagonist's HP can only drop as low as 1. The protagonist can use this aspect to their advantage by healing after a turn ends prematurely; this ultimately saves healing items.
- Human... It was nice to meet you. Goodbye. [Neutral]
- Now, now. There's no need to fight. Why not settle this... Over a nice cup of tea? [Genocide]
- I remember the day after my son died.
- The entire underground was devoid of hope.
- The future had once again been taken from us by the humans.
- In a fit of anger, I declared war.
- I said that I would destroy any human that came here.
- I would use their souls to become godlike...
- ...and free us from this terrible prison.
- Then, I would destroy humanity...
- And let monsters rule the surface, in peace.
- Soon, the people's hopes returned.
- My wife, however, became disgusted with my actions.
- She left this place, never to be seen again.
- Truthfully... I do not want power.
- I do not want to hurt anyone.
- I just wanted everyone to have hope...
- I cannot take this any longer.
- I just want to see my wife.
- I just want to see my child.
- Please... Young one...
- This war has gone on long enough.
- You have the power...
- Take my soul, and leave this cursed place.
- After everything I have done to hurt you... You would rather stay down here and suffer... Than live happily on the surface? Human... I promise you... For as long as you remain here... My wife and I will take care of you as best we can. We can sit in the living room, telling stories... Eating butterscotch pie... We could be like... Like a family... [Spare]
- No. That's just a fantasy, isn't it? Young one, when I look at you... I'm reminded of the human that fell here long ago... You have the same feeling of hope in your eyes. There is an ancient prophecy among our people... One day, a savior will come from the heavens. ...I believe the one that was prophesied was you. Somewhere in the world outside... There must be a way to free us from our prison. It pains me to give you this responsibility, but... Please. Take my soul... and seek the truth. Ha... ha... I'm sorry... I couldn't give you a simple, happy ending... But I believe your freedom... ...is what my son... ...what ASRIEL would have wanted. [If the protagonist refought Asgore and spared him twice]
- Why... You... [Genocide after being killed automatically in one hit]
- Flowey's Intervention
- So you finally get it. In this world... It's KILL or BE killed. [Kill]
- You IDIOT. You haven't learned a thing. Hee hee hee. In this world... It's KILL or BE killed. [Spare]
- <Name>. So you DO recall. In this world... It's KILL or BE killed. [Kill, if the Genocide Route was aborted]
- <Name>. You haven't learned a thing. Hee hee hee. In this world... It's KILL or BE killed. [Spare, if the Genocide Route was aborted]
- Hee hee hee. Did you REALLY think killing me would make a DIFFERENCE? No. Every time you load your SAVE, I'll come back. And every time you try to get a happy ending... I'll be there to tear it away! Ha ha ha!!! Well, let's get this over with. [Refight Asgore after killing Flowey]
- Hee hee hee. Don't worry. I know there's no REAL point in fighting you. The human souls would probably just revolt again. So...! [Refight Asgore after sparing Flowey]
- Let's just get this over with. [Refight Asgore #3]
- ... [Refight Asgore #4+]
- Flowey's Intervention (Genocide)
- See? I never betrayed you!
- It was all a trick, see?
- I was waiting to kill him for you!
- After all, it's me your best friend!
- I'm helpful, I can be useful to you I promise I won't get in your way I can help... I can... I can...
- Please don't kill me. [In Asriel's voice]
- Flavor Text
- ASGORE attacks! [Encounter]
- ... [Neutral]
- You quietly tell ASGORE you don't want to fight him. His hands tremble for a moment. [Talk #1, if the protagonist had not killed anyone]
- You tell ASGORE that you don't want to fight him. His breathing gets funny for a moment. [Talk #2]
- You firmly tell ASGORE to STOP fighting. Recollection flashes in his eyes... ASGORE's ATTACK dropped! ASGORE's DEFENSE dropped! [Talk #3]
- Seems talking won't do any more good. [Talk #4+, common]
- All you can do is FIGHT. [Talk #9]
- But there was nothing to say. [Talk, if the protagonist has gained EXP]
- You eat the Butterscotch Pie. The smell reminded ASGORE of something. ASGORE's ATTACK down! ASGORE's DEFENSE down! [Eating the Butterscotch Pie during battle]
- You tell ASGORE that he's killed you (number of times) before. He nods sadly. [Talk, if the protagonist dies to Asgore 1 - 4 times]
- You tell ASGORE that he's killed you (number) times. He nods grievously. [Talk, if the protagonist dies to Asgore 5 - 9 times]
- You tell ASGORE that he's killed you too many times to count. He nods pitifully. [Talk, if the protagonist dies to Asgore 10+ times]
- Asgore has low HP. [Low HP]