Hi, I'm here to question the logic of Mercy Stroke's "If delivered as killing blow, up to 20% of your maximum HP will be restored" additional effect.

The potency of the attack is not exceptional in any way, which means it literally has to be executed when your enemy has like <200 HP remaining.
Random lv 49-50 fodder enemy has ~2700 HP, which means Mercy Stroke needs to be executed precisely at <1% of enemy HP remaining to gain the benefit of the effect. And if you misjudge, you need to wait 40s as Marauder/Warrior or 90s as other class/job to try again.
Players are not able to know exact HP of enemies or even their %HP. This means there is no way to strategically use this ability. Another restraining condition is that it can be only used when enemy HP is below 20%. I call it bad game design.

The ability in this current form would be fine for turn based game where you can sit back, look at enemy HP, calculate/approximate how much damage Mercy Stroke will do, choose to either use Mercy Stroke or another ability/abilities that will not kill the enemy and make Mercy Stroke usable in the next round. If anyone remembers FFX battle system, this ability would fit in there just fine.
But not in action game with real time battles and you attacking enemies along other 3 (party), 7 (full party), 23 (alliance) or 50+ (FATE, any open world enemy) players. The level of coordination required is just unacceptable.

Here are several options how this should be handled:
- change additional effect to always occur
- if changing it so that effect always occurs is not possible due to game balance, make it so that there is ~30% chance the additional effect will execute
- if the above is not possible, change it so that you place a debuff on enemy for 15-30s and will regain the HP if enemy dies within 15-30s of using the ability
- change the additional effect to something else, something useful and strategically executable (an additional Damage over time on enemy, a brief Heal over time on player, 5-10% chance to instantly kill the enemy if damage of Mercy Stroke was not enough to kill it).

I'm actually a big fan of the 5-10% chance to instantly kill enemy if Mercy Stroke damage is not enough to kill it. Would fit so well with ability name. But would definitely not work on any bosses, which makes me sad panda

Anyways, what you think? Is Mercy Stroke currently useful beyond extra 200 potency damage? Do you ever delay/plan use of it to regain HP?