After you defeat Ghirahim's final form, you can save the game at the Bird Statue, and you can return to the present time using the Gate of Time to prepare. Then go back to the past and go to the bottom of the pit to enter the dark circle and begin the final battle.
In the first phase of the battle, you cannot charge up Skyward Strikes.
If you try to attack with your sword, Demise will block your attacks, so instead, wait for him to attack, and deflect his attack with a Shield Bash, then hit him. If your shield breaks, or if you have trouble with Shield Bashes, swing your sword at Demise from different directions until you land a hit, but do a backflip or side jump as necessary to dodge his attacks.
Sometimes when he reaches back with his sword, you may have enough time to hit him before he attacks.
If he is down on the ground, hit him as many times as you can before he gets back up.
Sometimes he will punch with his left hand. Try to Shield Bash or backflip away from this as well. He may also do a feint, where it will seem like he is about to attack, but will instead just swing his sword upward without actually hitting you.
If you get too far away, he will dash toward you and attack. Do a backflip to avoid this attack.
In the second phase of battle, Demise will charge up his sword with lightning. After Demise charges up his sword, he can shoot this energy at you like a Skyward Strike, but you can't block it with your shield, so for this first attack, run to the side to avoid it. Or, you can actually swing the bug net to knock the spinning energy back at him, which will stun him, allowing you to run up and attack him before he recovers.
The key to this phase of the battle is to watch for lightning strikes. You can raise your sword during lightning strikes to charge up a Skyward Strike. But if lightning is not striking, you cannot charge up a Skyward Strike, so don't raise your sword until you see lightning. If you wait too long after lightning starts striking, you might not be able to charge up a Skyward Strike when you raise your sword, so be prepared to dodge attacks until the next set of lightning strikes.
Once you have charged up a Skyward Strike, hit Demise with it as soon as possible. Depending on the timing, your Skyward Strike may cancel his out, or your Skyward Strike may hit him, stunning him momentarily. Whenever he is stunned, quickly run up to him and hit him repeatedly.
Whenever his sword is electrified, don't try to hit him with your sword, or you will get zapped. Instead, if he swings his sword at you, do three Shield Bashes in a row. If you deflect all three of his attacks, he will be knocked off balance, giving you a chance to hit him with your sword.
As before, if he dashes toward you, do a backflip to avoid his attack.
When Demise falls to the ground, do a finishing blow. You won't hit him in time, so repeat the above strategy to knock him down again. You have to be quick with the fatal blow the second time you knock him down, or he will recover before you can do it. Each time you knock him down, you get a longer window of opportunity to execute the fatal blow. Once you succeed, he will be defeated.
Congratulations! You won! While the credits are rolling, you can play the harp: just try holding different buttons and doing the strum motion until you get the harp to work. Be sure to watch the whole ending, including the post-credits scene. After "The End" appears on the screen, wait for a moment and then press any button. You will be asked if you want to start a new game in Hero Mode. In addition, in the Nintendo Switch version, whenever you start a new game in any save slot, you will be asked if you want to use Hero Mode for that save slot or not. In Hero Mode, the following changes add more of a challenge:
- Enemies have twice as much health
- Enemies deal twice as much damage
- Stamina gauge and air gauge run out more quickly
- Recovery hearts do not appear unless you are carrying a Heart Medal
- Skyward Strikes charge up more quickly.
- You start with all the bugs and treasures that you had before beating the game, which helps you get upgrades early on.
- The Thunder Dragon's lightning round includes 12 battles instead of the usual 9, adding the monster horde, the final Ghirahim battle, and the final Demise battle.
- Some dialogues are slightly different to reflect the changes in Hero Mode, such as the absence of recovery hearts.