http://lineage.pmfun.com/list/skill/c6/human-darkavenger.html
Horror - Active Magical - Range 600
http://l2p.l2wh.com/debuff.html
# Magic-based debuffs are affected by both the M.Atk. of the caster and the M.Def. of the target.
# The level of the skill affects the chance to land a debuff. I'm calling this Learn Level on L2P. Basically to ensure that a debuff will land, you need to keep the skill leveled up. In general, getting a debuff skill at level 70 will ensure that it lands normally on a target who is level 70, but has a reduced chance on a level 71 or higher and of course an increased chance on a level 69 or lower target. Specifically, it sets an effect multiplier which seems to correlate to a target's level similarly to accuracy & evasion. Skills like shield stun have an extremely high effect multiplier and skills like a tyrant's stun skill have a low multiplier.