Coup de Grace

They're pretty random, unfortunately. Later on, there's a Fan that increases the chance of getting Coup de Grace, as well as the Armamentalist' revocation medal which increases it even further.

Coup de Grace can randomly occur after taking any action, or when your character is attacked.

Each class has its own specific Coup de Grace. They never get "Better", but switching Vocations will allow you to get different Coup de Grace.

Warrior - Critical hit Every time
Gladiator - Cranks up the Tension to 50 or 100
Theif - Insure an item after battle (Common Drop only, I believe)
Paladin - Force all enemies to attack character, and protect character from all attacks
Armamentalist - Spins a Roulette Wheel that decides a random Multiplier on Experience gained in that battle

Those are just some of the Coup de Grace. The higher level your character is, the more turns they can keep the Coup de Grace before using it. They're mostly beneficial during boss fights.

If you can get all 4 characters with a Coup de Grace at the same time, you can unleash a Combo de Grace, which allows you to select from a list of possible combo moves. (I've never been able to do this myself, yet.)

I got close a few times when my characters were in the 40s-50s... got 3 CDG activated quite a few times, but it seemed like that last guy/girl didn't like teamwork lol.

quote Tenshi

If you can get all 4 characters with a Coup de Grace at the same time, you can unleash a Combo de Grace, which allows you to select from a list of possible combo moves. (I've never been able to do this myself, yet.)

Actually it's called "Co-op de grace",and you have to have everyone use thier Coup de grace on the same turn. When this happens,you get to choose between 4 moves (they depend on your vocations),and fortunately it tells you what they all do.

I've only gotten it once,and I used "Soul asylum" which made my entire party temporarily invincible.

quote Dragoon

does it just have to be 2+ people?

Good question,it would be much easier to activate with 2 members instead of 4. But if you did that,I bet it would only give you 2 options because you have less party members.

another co-op de grace turn all monsters into metal monsters but not bosses

Just managed to get my first co-op de grace, ironically against a mere lone golem. I was worried my warrior would screw it up with her coup de grace - instant critical hit - and kill the golem first, but the co-op de grace kicks in first. I was offered a four-character combo attack, replacing the enemy with metal monsters, making my team invincible or getting aid from a 'saintly ally'. Or I had the option of getting the four individual coup de graces instead. Went for the metal monster option, since the rest would have been useless against a golem, and the golem was replaced by two liquid metal slimes and two metal king slimes - first ones I've encountered in this game. The two LMSs fled but the MKSs hung around long enough for me to get in two critical hits. Woohoo!

That rocked.

Just my opinion... I don't really think any of the coup de graces are very epic. I mean,it's nice when a mage/sage can do a spell without wasting mp, but it basically disappears the next battle.