I have found during my farming that some mobs will take 0 damage while in reaction to certain situations making their defeat cumbersome for a normal mob.

First on the list and most frustrating is the toad's reaction to taking damage while charging "Gut Press". If the PC deals enough damage while the toad is charging the ability the toad will flip on it's back and wriggle around for a cool debilitation effect. However if the PC continues to attack, the damage that would normally kill the frog is simply given a "0" until the frog flips back over, then the PC has to deal 1DMG just to kill it simply because the frog cannot be defeated until the animation is completed.

Normally this would not be frustrating if I were to be fighting a single mob, but some leves require the simultaneous combat of 3-4 frogs, and the MP/TP/Time wasted on attacking a toad that will flip back over and have to receive 1DMG is dangerous and has costed me my life a number of times.

I believe it to be the same glitch that haunted the Moogle fights pre-patch.

Also, though slightly smaller issue.. if mob is using an ability that requires charging and an animation specific to that attack (Sheep's Lullaby bubble attack) and a PC stuns the mob just at the beginning of charging said attack, the mob will be invulnerable until the attack/animation (which has failed) is completed, which in the case of lullaby, can be around 15sec.

Thank you for viewing this and continuing to deliver upon your promises of a brighter future for FFXIV.