Improved attacks and sustained damage
1.5s after damaging a champion gain a large amount of attack speed. Lethal Tempo allows you to temporarily exceed the attack speed limit.
Excess healing on you becomes a shield.
Takedowns on enemies grant permanent Attack Speed.
Deal more damage to champion with more maximum health than you.
Empowered abilities and resource manipulation
Shortly after using your Ultimate, gain a decaying Movement Speed increase that lasts for 3s and allows you to pass through units.
While above 70% health, gain up to +40 Ability Power or +28 Attack Damage (based on level), Adaptive.
+9% Attack Speed
+5 AD or 9 AP
Aphelios is an ADC that relies heavily on his ability to auto attack rapidly.
Overheal synergizes incredibly well with Severum's healing.
More attack speed is always useful for Aphelios.
Most champions in the game will have more health than Aphelios, making Cut Down a huge boost to damage.
Nimbus Cloak's burst of movement speed is great when trying to escape from certain death.
Absolute Focus grants you a ton of extra AD, especially because you cant keep the buff active fairly easy with Severum.