Pyke easily able to proc the extra burst damage from Electrocute with a [Q]->[E]->Auto or [R] for massive burst and setup for an [R] execution.
WhySudden Impact
Pyke benefits massively form the extra Lethality after casting [E]'s dash for extra damage and execution setup.
WhyEyeball Collection
Pyke is naturally a snowballing assassin and as such relies heavily on his ability to snowball and actively pick up kills. Eyeball allows you to further push that into a bigger lead.
WhyUltimate Hunter
More [R] casts means more kills and more gold share with your teammates so that you can easily snowball the game to a victory.
WhyPresence of Mind
Presence of Mind is huge for keeping your [R] on a short cooldown. Mid Pyke is all about those huge executions with [R].
WhyLegend: Tenacity
Tenacity on Pyke mid can be the difference between a pentakill with [R] and dying instantly. Pyke needs to be able to get to his targets to be useful.