Main reason I made this guide is because the others don't talk about how to play Aphelios, so here's what I've learned so far in my experience carrying on PBE:

At the very beginning just begin using up your ammo until you have Gravitum, The Cannon. Once you have this, keep it as your Off Hand weapon and don't use it until you need a point and click CC - such as when your Jungler is coming.

All weapon's abilities have a way of consuming some of your Off-Hand weapon, making it easy for you to Q - W to switch to Gravitum - Q again with Gravitum to root.

Master this and you'll get through lane phase with a lot more gold than your opponent.

Only once you have Runaans and team fighting has begun can you use Gravitum as your main weapon.

Other combos:

Chakram + Sniper Rifle: Can create turrets that mark enemies and you'll be auto attacking the enemy from infinite range with high burst potential and maximum safety for you!

Chakram + Flamethrower OR Pistol: You'll want to use Flamethrower Q or Pistol Q to get Chakram stacks then switch to Chakram to keep the stacks up by attacking enemy champions. Chakram is the highest DPS for auto attacks if you can get the stacks for it. So, you'll want to get the stacks up and switch whenever they're expiring and keep swapping to be efficient.

Sniper + Gravity Cannon: If you use the Sniper Q and auto while Gravity Cannon is on your off-hand then you can make picks from long-range and snare people that are caught out. Usually requires a teammate nearby to capitalize on this method.

Flamethrower + Gravity Cannon: If the enemy is grouped up then you can use the flamethrower Q to apply Gravity Cannon's passive then switch to snare multiple people on the enemy team for 1.5 second and this usually leads to great wombo combo opportunities for you and your team!

Passive: The Hitman and the Seer

INNATE: Aphelios has access to an arsenal of 5 Moonstone Weapons, created by his sister Alune. He equips two weapons at any one time, one as his main weapon and one as his off-hand. Each weapon has a unique basic attack and passive effect.

Aphelios begins the game with Calibrum as his main weapon and Severum in his off-hand, with Gravitum, Infernum, and Crescendum queued in reserve. The queue order can be rearranged based on weapon usage.

MOONLIGHT: Weapons spawn with 50 Moonlight for ammunition, which is consumed on basic attacks or to cast his Q abilities. Abilities that cause Aphelios to attack do not cost additional Moonlight on top of their ability cost. Once his main weapon is exhausted of Moonlight, it is moved to the end of the queue and Aphelios equips the next available weapon from his reserve.

WEAPON MASTER: Aphelios cannot improve his abilities with skill points. He starts the game with Phase and gains access to Q abilities at level 2. He gains access to Moonlight Vigil Moonlight Vigil at level 6, which improves automatically at levels 11 and 16. Instead, Aphelios may spend his skill points to gain bonus attack damage, bonus attack speed or armor penetration.

---

Calibrum, the Sniper Rifle

INNATE: Aphelios gains 100 bonus range while Calibrum is his main weapon.

PRECISION: Enemies damaged by Calibrum via an ability are marked for 4.5 seconds, revealing them for the duration. Aphelios's next basic attack against a marked target uses the current off-hand weapon and gains Range icon global range.

This attack will consume all marks, dealing 20 / 25 / 30 / 35 / 40 (based on level) (+ 40% bonus AD) bonus physical damage per mark to the initial target. If Calibrum is the current off-hand weapon, the empowered attack uses the main weapon instead.

Moonshot

CALIBRUM - ACTIVE: Aphelios fires a bolt of energy in a line, dealing 60 / 85 / 110 / 135 / 160 (based on level) (+ 60% bonus AD) (+ 100% AP) physical damage to the first enemy hit.

---

Severum, the Scythe Pistol

INNATE: Basic attacks with Severum don't use projectiles.

RESURGENT: Severum's attacks heal him for 8% − 25% (based on level) of damage dealt.

Healing from Severum in excess of Aphelios' maximum health is converted into a shield for an amount of up to 10 − 140 (based on level) (+ 6% maximum health), lasting for up to 30 seconds.

Onslaught

SEVERUM - ACTIVE: For 1.75 seconds, Aphelios gains 20% (+ 10% per 100 AP) bonus movement speed and autonomously performs up to 6 (+ 3 per 100% bonus attack speed) attacks over the duration to the nearest enemy, prioritizing enemy champions.

Attacks alternate between Severum and his current off-hand weapon, each dealing 10 / 15 / 20 / 25 / 30 (based on level) (+ 35% bonus AD) physical damage, 25% on-hit damage and can critically strike. This will consume Moonlight from Severum regardless of whether the attacks are used.

---

Gravitum, The Gravity Cannon

INNATE - BINDING: Gravitum applies a 30% slow that decays over 3.5 seconds.

Binding Eclipse

GRAVITUM - ACTIVE: Aphelios expunges all enemies affected by Gravitum's slow, dealing 50 / 65 / 80 / 95 / 110 (based on level) (+ 35% bonus AD) (+ 70% AP) magic damage and rooting them for 1 second.

---

Infernum, the Flamethrower

INNATE - INCENDIARY: Infernum deals 110% AD physical damage to the target and spray four firebolts in a cone behind them, each dealing 75 / 100% (based on level) AD physical damage to enemies hit, reduced to 34 / 45% (based on level) AD physical damage against minions.

Critical strikes spray eight firebolts over a X% wider cone and deal bonus damage.

Duskwave

INFERNUM - ACTIVE: Aphelios unleashes a wave of energy in a cone, dealing 25 / 35 / 45 / 55 / 65 (based on level) (+ 80% bonus AD) (+ 70% AP) physical damage to all enemies hit and locking on to each of them. After a delay, Aphelios then fires a volley of basic attacks from his current off-hand weapon, one at each locked-on enemy. There is no range limit for locked-on targets.

---

Crescendum, the Chakram

INNATE: Basic attacks with Crescendum hurl the blade at the target, which lingers for 0.25 seconds before homing back to Aphelios. He is disarmed until he retrieves Crescendum, but the attack timer is reset once caught.

ARCING: Whenever Aphelios casts an ability that would require him to throw Crescendum, he instead throws a spectral Chakram at his target that similarly returns to him. Aphelios accumulates the Chakrams he catches, up to 20, which last for 5 seconds. Attacks against champions and epic monsters will refresh the lifespan on Chakrams.

Basic attacks with Crescendum deal 30 / X% AD (based on number of Chakrams) bonus physical damage. The bonus damage from Chakrams can critically strike.

Sentry

CRESCENDUM - ACTIVE: Aphelios deploys a lunar sentry for up to 20 seconds, reduced to 4 seconds after it starts attacking. Deploying a new sentry reduces the eldest's duration to 4 seconds. A sentry has 3 health, enemies can attack the sentry with basic attacks, dealing 1 damage per hit.

The sentry autonomously attacks the nearest enemy in range with a clone of Aphelios' current off-hand weapon, dealing 25 / 40 / 55 / 70 / 85 (based on level) (+ 50% bonus AD) (+ 50% AP) physical damage. The sentry can critically strike and benefits from Aphelios' attack speed and critical strike chance.

---

Phase

ACTIVE: W - Aphelios switches between his main weapon and off-hand weapon.

---

Moonlight Vigil

ACTIVE: R - Aphelios casts forth a lunar spotlight that stops upon illuminating an enemy champion. Alune smites the area centered on the illuminated enemy, dealing 125 / 175 / 225 (based on level) (+ 20% bonus AD) (+ 100% AP) physical damage and locking-on to each enemy hit.

After a delay, basic attacks will begin raining from the sky based on Aphelios' current main weapon, one upon each enemy locked-on by Moonlight Vigil. These attacks can critically strike for (50% + 18.75%) AD bonus physical damage. There is no range limit for locked-on targets.

Calibrum, the Sniper Rifle: Applies an empowered mark that deals 20 / 45 / 70 (based on level) additional physical damage per mark.

Severum, the Scythe Pistol: If at least one enemy is hit, Aphelios heals for 200 / 300 / 400 (based on level) health.

Gravitum, the Gravity Cannon: Enemies are slowed by 99% for the same duration.

Infernum, the Flamethrower: The initial blast deals an additional 50 / 100 / 150 (based on level) (+ 40% bonus AD) physical damage. Attacks splash in a circle instead of a cone. Enemies will take damage from overlapping areas.

Crescendum, the Chakram: 3 additional spectral chakrams return to Aphelios from the first enemy hit, for a total of 4, on top of those from other enemies hit.

This is my first guide ever, and I know I have a lot to add. I still need to play more Aphelios in Mid and Top to finish those guides.

Next I'll be adding tips on how to best use your abilities depending on situation and what two weapons you currently have.

My plan is to keep this purely tip based, rather than just copy pasting ability descriptions or generic stuff that applies to all champions.

Please let me know in the comments if there's anything in particular you'd like to see.