Guild Wars 2

Tested on:
o Class: Warrior
o Weapon: Spear
o Ability: Impale(No 1)(Happens with all but Harpoon Pull, explained bellow)
o NPC: Electric Fish(lvl 52) and Barracuda (Have not tested on others)
o Zone(s): Sanguine Bay, Blood Tide Coast & Queensdale.

Bug:
To recreate this Bug the player must be Under and Behind the NPC before attacking. The NPC will turn around and begin attacking the player at this point but does not move down or up in the water. It seems that if the player continues to attack from the same position without moving the mob evades after around 75% health in my case and returns to its place, then regains full health and is able to be attacked again, for the duration of the evasion the NPC is fully invulnerable to damage, I had it happen once on almost all Underwater Creatures, but the ones listed above are the ones i consistently tested this bug on, it does not break the game but can be frustrating if players don’t realize that attacking a mob from their back and directly underneath them causes this.

Other things to consider:
My Warrior has allot of Toughness and Healing, if this in any way interferes with the way that NPCs A.I. is coded, for the duration of my testing and the duration of most underwater fights against this type of NPCs my health never reaches bellow 98% due to constant healing from Healing Signet and low damage dealt and sometimes multiple missed hits by the NPC. So far have only been able to recreate it while attacking from behind and under the NPC slightly being in melee range but as far as i can get from it.