First of all I'm not a pro player - I dont even play rankeds so often.
I was playig a lot of leauge in 2018-2019. And quit for some time but got to the gold division in s11 and s12. So you can classify me as Silver/Gold player.
This build is created just to have fun - but it works increibly well - I often got a decent stats on Evelynn and huge impact on the game.


So the way it works is her movement speed and tankiness. The enemies does not expect you to take so much dmg (and deal twice as that). The phase rush are great for both chasing, escaping and most importantly poking. YOU should stand close to the enemy all the time and spam your Q and E. Use R to finish the target or escape.

The Heartsteel not only makes you bigger (with is super fun in late game) but also deals physical damage on-hit scaling with your HP. (in mid game Heartsteel should deal around 400 per hit). Your E procs on-hit so not only it does your basic AP dmg but also Heartsteel AD damage. Demonic Embrace deals damage based on max hp (you'll deal biggest damage beacause Evelynn is melee champion.) but also adds AP based on your HP. And this is crucial. The third item should always be Rabadon.
The huge amount of AP that Deathcap is providing is just crucial for dealing damage.

You can build either Heartsteel or demonic embrace first. Heartsteel if you are feed and dominating in the lane. And demonic embrace is you are losing.

At the end you can build the tank item of your choice or simply buy other AP items such as Lich Bane or Cosmic Drift.

This build is extremly fun to play but I do not recommend it to play on Ranked. I played few ranked with it got some wins and some loses but I was not feed or stomped. It just some people might troll or harras you for playing something off-meta such as Eve mid.