Aphelios has 5 different activated abilities, based on his equipped weapon:
Calibrum (Rifle): Fire a long range shot that deals 60/85/110/135/160 (+ 42% bonus Attack Damage - 60% bonus Attack Damage)(+ 100% bonus Ability Power) physical damage to the first enemy hit and marks them for a long-range follow-up attack.
Severum (Pistol): Gain 20 (+ 10% per 100 ability power) movement speed and fire both weapons at the nearest enemy for the next 1.75s. Deals 10/15/20/25/30 physical damage (+ 21% bonus Attack Damage - 30% bonus Attack Damage) over 6 (+3 per 100% bonus attack speed) shots. Prioritizes champions. Applies on-hit effects at 25% damage.
Gravitum (Grav Cannon): Expunge this weapon's slow on all targets, rooting them for 1s and dealing 50/65/80/95/110 (+ 26% bonus Attack Damage - 35% bonus Attack Damage)(+ 70% bonus Ability Power).
Infernum (Flamethrower): Spout a wave of flame, dealing 25/35/45/55/65 (+ 56% bonus Ability Power - 80% bonus Attack Damage)(+ 40% bonus Attack Damage) physical damage. Then, attack each enemy hit with your secondary weapon.
Crescendum (Chakram): Deploy a lunar Sentry equipped with Aphelios' secondary weapon, lasts 20s. Sentries activate when an enemy approaches and fire at them for 31 - 100(+ 40% bonus Attack Damage - 50% bonus Attack Damage)(+ 60% bonus Ability Power) physical damage per shot over 4s. Sentries benefit from attack speed and critical strike.