Ragnarok Online 2 Threat Gain and Taunt Guide by Ryouichi

From iRO2 Threat Meter:

All action gain threat by 1 point.

Aggro gets you threat by 1 point.

1 damage = 1 point of threat.

1 heal = 1 point of threat.

DoT shows up on threat. Each DoT shows up as additional threat. (Tested with Head Crush, Oratio, and Wild Crush).