I finally managed to defeat Cor, and in just under five minutes, by following these steps/guidelines, many of which I've learned from watching various other YouTubers who posted their victories:
1. At the beginning of the fight, even before the mission text fades off the screen, lock onto Cor with
and then, with
still held down, hold the movement analog stick down and press
to attack with a Sword Throw/Strike Raid from across the map. Then, get ready to start blocking his attacks.
2. Don't use any Glaive Arts (
) until the Valor bar is full. Towards the end of the fight, he will go into a glowing red rage far longer and more frequently, so it will be hard to attack him. So as soon as your Valor bar is full, preferably when he's vulnerable from a counter-attack or at low health or both, use Maelstrom to deal him a lot of damage. Then make sure not to press
again until right when the "Dual Master
" prompt comes up. If you do, Dual Master should finish him off.
3. If you want to win, the majority of the fight will involve blocking most if not all of his attacks. Make sure to block Cor's attacks with your shield (
), preferably in short, controlled bursts so you don't deplete the stamina bar and so you'll have a better chance of counter-attacking. You'll want to wait until just before he attacks to block so you can fill up your Rage bar better and more importantly so you can counter attack. Usually, he will block your counter attack, unless you're countering one of his blue attacks, or occasionally when you counter a close-range kunai throw. It will be hard to get the hang of how to block at just the right times, so spend time practicing to get it right, and don't get discouraged if you block him a little too early and can't counter or too late and take some damage. Occasionally, I've noticed successful blocking may reimburse your HP for a recent attack, but I haven't really figured out how or when, so don't count on it. (It might be that pressing
right after being attacked restores the HP you lost.)
4. Many of his attacks, particularly the blue ones, will be preceded by a short battle quote like "You're mine!". You'll want to block less then a second after he ends his battle cry, because that's when he'll usually attack you. When you do counter-attack one of his blue aura attacks, he'll be weakened for a few seconds, and that's when you'll be dealing the majority of the damage you'll do to him. Preferably, you'll want the rage bar to be at 3x or 4x when that happens to deal as much damage as possible. If you're fast, you'll be able to deal just enough attacks that the on-screen attack chain number will count five attacks in a row, give or take one. After that, he'll be back to his old self again, so be ready to keep blocking his attacks.
5. If Cor glows red, it means all his attacks can't be blocked and will bust through your shield, so just do a zig-zag Dodge Roll (
+ movement analog stick) away from him all around the map until he calms down again. Often, he will glow red as a result of the player blocking his attack too early to counter it. If Cor is down to around 1/2 health or less, failure to counter-block a blue attack will result in him going into a red rage for around half a minute, so at that point in the fight, work extra hard to counter it if you can, and run away if you don't.
6. Press
to use a potion whenever your health goes below 2000, and if you are KO'd, make sure to press
to use your Phoenix Down if you haven't already. Phoenix Downs not only restore you from 0 HP to full health, they also slowly regenerate your HP for a short time. As long as you have a little red fireball swirling around you, your HP will gradually restore, but the fireball won't stay there forever, and once it's gone you'll stop regenerating. You only get 3 Potions and one Phoenix Down, so use them wisely.
7. Make sure to face in Cor's general direction throughout the match, except when he's glowing red. If you're not facing him, your blocks might fail because your shield's in the wrong direction, and because it's harder to see when he's attacking like that. If you're having trouble spotting him, use
to lock onto his position.