Guild Wars 2

Hey… What’s the bar under the target’s health bar for? The one that looks like a screw?

It’s the new defiance system. Every time the enemy is charging up an attack you are able to stop, the bar turns light blue. After that all crowd control type skills (like taunt, fear, blind, knockback etc) removes a portion of the bar. If you deplete the entire bar before the attack goes off, something happens to the enemy. For example the mob you took this screenshot of gets stunned for several seconds.

This bar right here.

Defiance bar

Thanks Invictus, Bovan