Asgore and Flowey are among the final boss fights of Undertale, coming after you've explored The Core.
The following boss is designed to be played as part of a complete Pacifist guide - in short, going through the entire game without killing anything to unlock a different ending - of which bosses are some of the hardest to beat.
If you're playing a Genocide run, however, you'll be fighting someone different in the final encounter - the prior link explains who. But whichever way you're playing, our wider Undertale walkthrough delves into other areas of the game.
Asgore boss fight
As the battle begins, Asgore will destroy your Mercy button. This time you have no choice but to fight to the bitter end!
His attacks are very similar to Toriel's but they do significantly more damage, but you can eat your Butterscotch Pie and Talk to him three times to lower his AT and DEF to even the odds a little if you need to.
- When he swipes his hands across the box move to one side then squeeze through the gaps in the flames.
- Stay near the middle of the box for his rings of fire, and only move as far as you need to to squeeze through the gaps.
- Stay in the middle of the box during his spiral fire attacks, and move left and right in time with its rotation.
The longer the fight goes on the more damage you'll do to him with each hit, and he will eventually concede defeat.
Choose to spare him, and Flowey will make an appearance. At the end of his rant the game will crash (at least, on PC) and when you reload it your save file will be "corrupted" - don't panic, it's meant to happen! Just pick Continue, and prepare for an epic battle...
Photoshop Flowey boss fight
This fight is very different to any you've faced before. There's no box constraining you, the fight isn't turn-based, and to start with you have no buttons along the bottom of the screen; the Fight button will show up occasionally, and you need to hit it quickly when it appears.
Flowey's attacks cycle between an all out assault and a short battle against one of the six Souls. Dying at any point will cause the game to quit, but at the end of each cycle you'll hit a checkpoint so if you die you can at least resume the battle where you left off.
During his all out phase the most important thing to do is keep moving - as long as you don't stop you won't die, you'll just get taken down to 1HP.
- When small circles appear at your location move out of them as they shrink.
- Move left and right when he fires his orange and white criss-cross beams.
- When he uses his flamethrowers move up as high as you can and slide left and right to keep moving.
- His rain of bombs require some nifty manoeuvring to avoid - try and stay in the gaps between them and move with them as much as possible.
- The bouncing spiky balls are fairly easy to dodge - move to the bottom of the screen and follow the gaps as they bounce around.
Once you've survived a wave and hit the Fight button, he'll bring out a Soul.
At a random point during this phase an Act button will move across the screen that you must activate - hitting it will turn his attacks into healing items which should get you back to full health, but failing to do so will get you killed pretty quickly.
- Light blue soul: Dodge the whirling blades. The Act button will fall from the top of the screen.
- Orange soul: Boxing gloves will circle around the screen, moving in and out as they do so. The Act button will again drop from the top of the screen.
- Dark blue soul: Stay as low as possible, and duck underneath the shoes as soon as you get the chance. The Act button will take the place of one of the shoes and move in from the side.
- Purple soul: Words will float in from either side of the screen, so just stay in the middle and just move up and down to dodge them. The Act button will also float in from the edge and should be easy to hit.
- Green soul: Stay low and move from side to side to avoid the flames spewing forth from the frying pans. The Act button will leap out of one of them.
- Yellow soul: Stay clear of the area between the gun and the target and you'll easily avoid taking damage. The Act button will fire out of the gun.
Playing Undertale? Our complete Undertale walkthrough and Pacifist guide will explain how to finish the game while sparing everyone, covering all areas including the Ruins, Snowdin, Waterfall, Hotlands and The Core and more. You can also learn about how to unlock every Undertale ending and all Undertale Trophies, access hard mode and play the game in the most evil way possible with a Genocide run.
Once all six souls have been dealt with Flowey's DEF will drop to zero and your HP will be fully restored.
He'll fall back on his all out attacks but the souls will continue to throw out healing items, so providing you hit the Fight button every time it appears the fight should be over fairly quickly from here.
The game will come to a conclusion at this point, but if you managed to not kill any monsters and befriended Papyrus and Undyne as part of a Pacifist playthrough, there's more to come. Reload the game and head to the Laboratory to see even more.