Shadow Walk (Passive)
Evelynn fades away into the shadows. She can only be seen by nearby enemy Champions or true sight
While in stealth, Evelynn regenerates 1% of her max Mana every second
Casting spells, taking damage, or dealing damage unstealths Evelynn for 8 seconds

Hate Spike
19/23/27/31/35 Mana, 1.5 second Cooldown
Evelynn fires a line of spikes through a nearby enemy, dealing 40/60/80/100/120 (+0.45 Ability Power) (+0.4 bonus Attack Damage) magic damage to all enemies in its path
Hate Spike prioritizes what Evelynn has attacked recently

Dark Frenzy
No Cost, 20 second Cooldown
Passive: Evelynn's spell hits on enemy Champions grant her 4/8/12/16/20 Movement Speed for 3 seconds (effect stacks up to 4 times)
Active: Evelynn removes all slows affecting her and gains 30/40/50/60/70% Movement Speed for 3 seconds
Champion kills and assists refresh Dark Frenzy's cooldown

Ravage
50/55/60/65/70 Mana, 9 second Cooldown
Evelynn slashes a target enemy 2 times, dealing 35/60/85/110/135 (+0.5 Ability Power) (+0.4 bonus Attack Damage) magic damage with each strike
Evelynn then gains 60/75/90/105/120% Attack Speed for 3 seconds
Agony's Embrace
100 Mana, 150/120/90 second Cooldown
Evelynn impales all enemies in the targeted area, dealing 15/20/25% (+1% per 50 Ability Power) of their maximum Health in magic damage and slowing their Movement Speed by 30/50/70% for 2 seconds
Evelynn siphons their pain, gaining a 150/225/300 health shield for each enemy Champion hit which lasts up to 6 seconds

I don't like scrolling through pages of lore and feelings to get to the meat and potatoes of how the OP intends to play the champion.

My intentions with this build is to be a flanking assassin to grief their retreat. This champion is not strong enough to lane solo since its mainly a burst nuke then you will be oom. I have seen AD builds for her but it seems her Q will benefit more from AP which will be spammed with an E and a R to finish if available. I think that Evelyn will also be a poor choice for minion farm since she can't sustain a lane and range is an issue.

Until L18 you don't want to be in team fights. You would be better suited hunting down the loaner pushing a lane since he/she will likely not have wards behind them, and you can cut off his retreat to the base.

Please leave constructive crits or just flame away. I made this more as a guide for myself to have up and tweek as the opponents change. Thanks for looking.

I think my progression of items is self explanatory and I broke it down by the actual purchases I would make. However the final item is a mystery to me. I doubt I will ever be ingame long enough to get a 6th item made, however since cooldown reduction is already staggering (imagine a 40-50s cooldown on Agony's Embrace) lets get that gunblade if we are still fighting