Combination skill system merges skills of same type into one passive skill or innate ability that can be customized by player by investing into synergy passives. This makes each skill unique(similar to ) but doesn't allow more than one skill of same type(unlike the variable-component system).

Old system:Multiple Aura skills: Various auras with different effects.
New system: One passive(always-on) aura with upgradeable components:
Aura Range(passive, adds 1 range per level in skill), Auric Healing(passive, adds +x healing to aura),Auric Fire(Adds fire damage, passive),Auric Speed(passive, makes aura pulse faster),etc.

Old system:Multiple bow-related skills(ex:Diablo2) with different costs/effects.
New System: Arrow passives: Each of passive skills adds effect to basic arrows(as Diablo2 Pierce skill).
Guided Arrow-> Guiding Projectile skills(increase angle of guided projectile from e.g. angle of 5 to 180 (track everything)(
Immolation Arrow->Projectile Fire passive(adds more fire damage and firewall-like effects)

Old system:Multiple magicBolt projectile(Firebolt, Icebolt, Lightning bolt)
New System:one Magic Bolt projectile skill with synergy from Fire Mastery(passive,add +x fire damage, +y% fire damage), Ice mastery,Lightining mastery,etc each of Mastery skills adds damage to all spells of that element( Magic Bolt just becomes one of abstract projectile types, which benefit from mastery passive skills).