Is not Hack. Just wrong setup server.
Look Default L2J Gracia 2 setup
# Alternative success rate formulas for skills like dagger/critical skills,
# 'true' to use this formula , 'false' to use the original based on rCrit (c3 like)
AltGameDaggerFormula = False <-True For Custom
# Alternative success rate for skills like dagger/critical skills
# MUST be setted above to AltGameDaggerFormula = true
# Rate of success is based on the position of the char,to this is added/subed some percent
# if the char is behind or is in Front of the target.
# FailRate is the chance of a skill critical attack to fail. max value 100 (100% fail)
# Successrate is the chance of a skill critical attack. max value 100 (100% critical)
# Do some tests before changing the values.
AltSuccessRate = 0
AltFailRate = 30
AltSuccessRateBehind = [glow=red,2,300]15[/glow]
AltSuccessRateFront = 10
# Dagger Skill Damage VS heavy, light, robe.
# Use value 1.0 to disable this option. Higher value equal to lower damage.
DaggerVSRobe = 1.8
DaggerVSHeavy = 2.5
DaggerVSLight = 2.0
# Instant Kill Effect lvl 2 (no change on CP, HP reduced to 1hp, no kill on char)
# Value In Percent %, higher value, higher chance, max value = 100%.
InstantKillEffect2 = [glow=red,2,300]2.0[/glow]