Hello guys! Its misterfirstblood from EUW and today i wanna show you how I play Aphelios and give you an introduction and basic guide for this champ and how you should play Aphelios.
Be aware, he might be one of the most complex champions of all time since he carries 5 weapons with 5 different abilities and basic attacks with him.

+ A huge variety of abilities that can come in handy more or less
+ CC, AoE, Lifesteal, Waveclear all build in to his kit
+ Very strong if you master him

- Nerfed pretty hard on the current patch, low winrate and a super complex design aren't a good combination for beginers to enjoy playing Aphelios
- A bit RNG on which weapons you have and which ones you need currently
- Super hard to master
- Good Opponents can play around your current weapons and since you have to use some Ammo to receive Lasthits they can punish you pretty hard
- No mobility tool

Instead of explaining the abilities we rather explain the different weapons of Aphelios in that case, since he has no E Ability, his W is basically a weapon swap and his ult and Q highly depend on which weapons he is carrying with him.
I just copy paste the ability descriptions here because it would be way to much text and my english grammar might be too bad to explain everything as in depth as the database text describes it.

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

Innate - Moonlight: Weapons spawn with 50 Moonlight for ammunition, which is consumed on basic attacks Pix, Faerie Companion on-attack or to cast his abilities 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 assembles his next available weapon over 1 second to equip it from his reserve, with its Q. ability being placed on a 1.5-second Cooldown cooldown before that time. Aphelios cannot cast Phase Phase during the assembly.

Innate - Weapon Master: Aphelios cannot improve his abilities with skill points. He starts the game with Phase Phase and gains access to abilities abilities at level 2 and Moonlight Vigil Moonlight Vigil at level 6, with the latter improving automatically at levels 11 and 16. Instead, Aphelios may spend his skill points to gain Attack damage bonus attack damage, Attack speed bonus attack speed or Armor penetration lethality.

Q:


The active effect of Aphelios' Q varies based on his current main weapon.

The individual actives do not share a cooldown.

W: Calibrum, the Sniper Rifle


Aphelios gains Range icon 100 bonus attack range while Calibrum is his main weapon. Enemies damaged by Calibrum via an ability are marked for 4.5 seconds, Reveal icon revealing them for the duration. Aphelios' next basic attack against a marked target uses the current off-hand weapon and has Range icon 1800 range, bonus missile speed, and a brief cast time that lasts shorter based on Aphelios' proximity to the target.

This attack will consume the marks from all targets, dealing 15 (+ 20% bonus AD) bonus physical damage to the main target for each mark consumed. If Calibrum is the current off-hand weapon, the empowered attack uses the main weapon instead.

"Calibrum."
Moonshot
TARGET RANGE: 1450
WIDTH: 120
SPEED: 1850
CAST TIME: 0.4
COST: 10 Moonlight + 60 Mana
COOLDOWN: 10 − 8 (based on level)
Moonshot

Active: Aphelios fires a bolt of energy in the target direction that deals 60 − 160 (based on level) (+ 42% − 60% (based on level) bonus AD) (+ 100% AP) physical damage to the first enemy hit.

Severum, the Scythe Pistol


Basic attacks with Severum are Projectile non-projectile and have an Relentless Force 2 uncancellable windup. Severum's attacks Heal power icon heal Aphelios for 2.5% − 9% (based on level) of the post-mitigation damage dealt, increased to 7.5% − 27% (based on level) for attacks from abilities.

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

"Severum."
Onslaught
EFFECT RADIUS: 550
CAST TIME: none
COST: 10 Moonlight + 60 Mana
COOLDOWN: 10 − 8 (based on level)
Onslaught

Active: Aphelios enters an onslaught for 1.75 seconds, gaining 20% (+ 10% per 100 AP) Movement speed icon bonus movement speed and autonomously performing up to 6 (+ 2 per 100% bonus attack speed) attacks over the duration against the nearest Sight icon visible enemy, prioritizing enemy Champion icon champions.

Attacks alternate between Severum and his current off-hand weapon, each dealing 25% On-hit icon on-hit damage and 10 − 40 (based on level) (+ 20% − 35% (based on level) bonus AD) physical damage, affected by Critical strike icon critical strike modifiers.

Aphelios cannot cast Phase Phase nor Moonlight Vigil Moonlight Vigil during Onslaught, but he is still able to move. He cannot perform attacks while unable to declare basic attacks.

Gravitum, the Gravity Cannon
Gravitum, the Gravity Cannon
COST: 1 Moonlight per attack
Gravitum

Attacks with Gravitum Slow icon slow enemies by 30% for 3.5 seconds, decaying to 10% after 0.7 seconds.

"Gravitum."
Binding Eclipse
EFFECT RADIUS: Global
CAST TIME: 0.3
COST: 10 Moonlight + 60 Mana
COOLDOWN: 12 − 10 (based on level)
Binding Eclipse

Gravitum Gravitum - Active: Aphelios expunges all enemies with Gravitum's Slow icon slow debuff, dealing 50 − 110 (based on level) (+ 26% − 35% (based on level) bonus AD) (+ 70% AP) magic damage and Root icon rooting them for 1 second.

Binding Eclipse also empowers in-flight Gravitum projectiles to instantly affect their targets upon hitting them.

Infernum, the Flamethrower
Infernum, the Flamethrower
COST: 1 Moonlight per attack
Infernum

Infernum shoots a firebolt at the target enemy unit, dealing physical damage to enemies it passes through. Upon reaching the primary target, the firebolt splits into a cone of 4 missiles behind it that deals physical damage to enemies hit. The firebolt deals 110% AD physical damage to the primary target and 82.5 / 110% (based on level) AD physical damage to secondary targets, reduced to 25.3 / 33% (based on level) AD physical damage against Minion icon minions.

Critical strike icon Critical strikes also apply to damage against secondary targets and spray 6 missiles in a 50% wider cone that deals Critical strike damage icon critical damage.

"Infernum."
Duskwave
TARGET RANGE: 650
ANGLE: 40°
CAST TIME: 0.4
COST: 10 Moonlight + 60 Mana
COOLDOWN: 9 − 6 (based on level)
Duskwave

Active: Aphelios unleashes a wave of energy in a cone in the target direction, dealing 25 − 65 (based on level) (+ 56% − 80% (based on level) bonus AD) (+ 70% AP) physical damage to all enemies hit and locking on to each of them. After 0.25 seconds, Aphelios then fires a volley of attacks from his current off-hand weapon, dealing 100% AD physical damage and applying On-hit icon on-hit effects at 100% effectiveness to each locked-on enemy. The damage is affected by Critical strike icon critical strike modifiers. There is no Range icon range limit for locked-on targets.

Crescendum, the Chakram


Basic attacks with Crescendum hurl the blade at the target, which lingers for 0.25 seconds before homing back to Aphelios. He is unable to declare basic attacks until he retrieves Crescendum, but the attack timer is reset once caught.
Crescendum 2

Whenever Aphelios casts an ability that would require him to throw Crescendum, he instead throws a spectral Chakram at the target that similarly returns to him. Aphelios accumulates the Chakrams he catches, up to 20, which last for 5 seconds or until Crescendum is out of Moonlight. Attacks against Champion icon champions will refresh the lifespan on Chakrams.

Basic attacks with Crescendum are empowered to deal 0% − 138.5% (based on number of Chakrams) AD bonus physical damage and have a 10.67% wind up percentage, decreased to 6.67% when Critical strike icon critically striking. The bonus damage from Chakrams can critically strike.

"Crescendum."
Sentry
TARGET RANGE: 475
EFFECT RADIUS: 500
CAST TIME: 0.25
COST: 10 Moonlight + 60 Mana
COOLDOWN: 9 − 6 (based on level)
Sentry

Active: Aphelios deploys an Untargetable icon untargetable lunar sentry at the target location that arms after 0.35 seconds, lasting for up to 20 seconds and granting Sight icon sight of its surroundings. The sentry attacks if an enemy gets in range, reducing its duration to 4 seconds and becoming targetable. Sentries have 6 health and take 3 damage per Ranged role ranged basic attack and 4 damage per hit by abilities. Turret icon Turret attacks kill sentries instantly.

The sentry autonomously attacks the nearest Sight icon visible enemy in range with a clone of Aphelios current off-hand weapon at 0.8 attack speed, dealing 31 − 100 (based on level) (+ 40% − 60% (based on level) bonus AD) (+ 50% AP) physical damage. The sentry can Critical strike icon critically strike and benefits from Aphelios' Attack speed icon attack speed and Critical strike chance icon critical strike chance.

W. Phase
Active: Aphelios switches between his main weapon and off-hand weapon over 0.25 seconds.

The icon of this ability reflects the next weapon that is in reserve.

Active: Aphelios receives a text prompt of the weapon Alune will create next.

E: Aphelios has no E Ability

R: Moonlight Vigil

Active: Aphelios casts forth a lunar spotlight in the target direction that briefly grants Sight icon sight of the area along its path and stops upon illuminating an enemy Champion icon champion. Alune smites the area centered on the illuminated target, dealing 125 / 175 / 225 (based on level) (+ 20% bonus AD) (+ 100% AP) physical damage to enemy champions struck and locking-on to each target hit, as well as granting Sight icon sight of the area for 2 seconds.

After 0.3 seconds of the illumination, attacks will begin raining from the sky based on Aphelios' current main weapon, dealing 100% AD physical damage and applying On-hit icon on-hit effects at 100% effectiveness upon each target locked-on by Moonlight Vigil. These attacks can Critical strike icon critically strike for (20% + 35% 35%) AD bonus physical damage. There is no Range icon range limit for locked-on targets.

Calibrum Calibrum: Applies an empowered mark that deals 50 / 80 / 110 (based on level) bonus physical damage per mark.

Severum Severum: If at least one enemy champion is hit, Aphelios Heal power icon heals for 250 / 350 / 450 (based on level).

Gravitum Gravitum: The initial Slow icon slow is increased to 99% and Binding Eclipse Binding Eclipse will Root icon root for 1.35 seconds instead.

Infernum Infernum: The initial blast deals 50 / 100 / 150 (based on level) (+ 25% bonus AD) bonus physical damage. Attacks Umbra Blades splash in a 400 unit circle instead of a cone, dealing「 90% of that damage. 」Enemy champions will take damage from overlapping areas.

Crescendum Crescendum: 5 additional spectral chakrams return to Aphelios from the first enemy champion hit, for a total of 6, on top of those from other enemies hit.

Since you dont really skill your abilities, rather stats you can decide between (Attack damage, attack speed, or lethality) you want to maximize Attack damage (Q) first, Lethality (E) second, and Attack speed (W) very last.
Theres not much to say about that.

Immortal Shieldbow and Galeforce are the most common Mythical item options on Aphelios. Since he has no mobility at all i really love Galeforce on him the most.
The next best items to increase your damage outcome will be Phantom Dancer and Infinity Edge but if you need lifesteal Bloodthirster is your next best item choice.
Lord Dominik's Regards is your key piece if you cant deal with the tanks currently while Mercurial Scimitar and Guardian Angel are your more defensive options.
If you need more critical strike chance since defensive options and tanks arent a Problem in your current situation Rapid Firecannon or Runaan's Hurricane will increase your critical strike rate and damage outcome significantly.

I figured out that Aphelios is one of the few exceptions Press the Attack works pretty well with. Especially with your Severum it is triggered in no time and dealing tons of damage to a single opponent.
Presence of Mind is just generally good to have and Legend: Bloodline increases your sustain while laning. I think its the best rune to have in that slot on the current patch, but if you need more attack speed feel free to pick alacrity.
Coup de Grace adds some more damage to your Kit and is the most generic choice in that row.

Domination as your second tree offers even more sustain and some Cooldown reduction for your galeforce. This is only interesting if youre planning to build it but i love Ingenious Hunter on him as well as Taste of Blood for a bit saver laning.

There is so much to talk about Aphelios but it pretty much comes always down to the fact that you have to play him a lot to understand his different interactions between various weapons.
But i give you some of the most basic Tips i can think of in the moment:
- If you use Severum, you dont shoot projectiles so you can attack Yasuo through his wind wall
- Always keep in mind what secondary weapon you are using so you can benefit from using your Q ability for example to lifesteal or land a Root on your opponent, even if your Gravitum Ammo is almost empty
- If you spend 49 Ammo and only have 1 left, you can still use your ability that needs 10 Ammo to use, so you basically used 59 if you play it correctly and want to make the most use out of it.
- The Crescendum Active can be used in Brushes to grant vision.
- You can use your Q with your current weapon, swap to another weapon and use Q again. If both of your weapons are just at 10 or less Ammo, you get 2 new weapons and can use 5 Abilities in a row + your ultimate, which is a deadly amount of burst damage and CC effects.
- At level 18 you get 33 Lethality for free, which other AD Carries normally wouldnt. You can ignore a lot of your opponents squishys armor stats with aphelios what really makes him shine in lategame.

Thats it for now. If i really wanted to go in depth here this would result in walls of text that noone could really understand.
Keep practising Aphelios and you soon will understand the rotations and interactions between his weapons better and better!

Thank you for paying attention to my guide!

If you found any mistakes please let me know, english is just my second language and i really tried my best here.