Combo skill can be used by Blade Knights only. This skill is enabled after completing the Ring of Glory and Dark Stone quest. Combo skill consists of 3 skills used together. There are 6 ways a combo can be produced: Weapon skill > Twisting Slash > Death Stab
Weapon skill > Twisting Slash > Rageful Blow
Weapon skill > Rageful Blow > Twisting Slash
Weapon skill > Rageful blow > Death Stab
Weapon skill > Death Stab > Twisting Slash
Weapon skill > Death Stab > Rageful Blow
Using these skills consecutively will produce a Combo.
In a nutshell, the first skill must always be a Weapon skill. The following two skills are to be skills from orbs (Twisting Slash, Death Stab and Rageful Blow).
Hint: Depending on which combo you want to use, you can set the hot keys of the skills in the order of 1, 2 and 3