Cor's central gameplay is around TWO of his buffs. TLDR: Maintain these buffs as much as possible! For high damage windows, leverage Cor's LD, since it isn't tied to a special buff/debuff. Then use his Reaper's Gale attack.
Cor's linked attack uniquely goes off before anyone's turns...
Reflorescere (LD) is primarily used for damage windows, as it grants an instant turn, and maxes out his stacks of his overhead effect.
His overhead is counts up by 1, max 10, whenever Cor triggers his start of turn attack.
At 7 stacks he gets a hard hitting, instant turn HP+ called Reaper's Gale. This is notable as each hit will hit the BRV DMG Limit, and it's instant turn. You drop down to 0 after using it. So if you want to take a few turns in a row you would loop LD -> Reaper's Gale -> LD and so on as you'd like.
Moonlit Dawn (S1) is a party battery + single target attack. Given it has 2 BRV dumps and a splash mainly used for single target fights.
Snowbreak (S2) also batteries the party but has an AoE attack. This skill is good for also upkeeping his Crownsguard Warrior buff along with damaging multiple enemies.
Lion's Roar (EX) recharges in 2 skill uses. It grants him his One of Lucis's Three buff.
BT (BT) grants the party good auras such as HP DMG Limit, but it also lets Cor link to both allies now without taking his Oath buff away. This is very powerful in counter/trap teams as ALL attacks will make Cor attack 3 times before the enemy strikes.
Welcome Coincidence (FR) with pretty easy conditions:
+5% for any off-turn attack
+40% when the active party member deals at least 1 BRV hit for 9,999 DMG or more
It also has some added party auras and a selfish aura enabling ANY of Cor's BRV hits to deal it's BRV DMG Limit (40% chance each hit)
Probably won't be the main FR outside of necessity, but FR Boards making Echoes a big hit while maintaining FR turn count is a huge compensation.