Now look, I'm a boosted Silver II scrub, but people and guides here helped me a lot with different champs and I wanted to pay a favor back, I absolutely love Ekko, he's so fun to play, and I love his confidence, dat boi sais "Won this fight already, doing it again for fun" like come on.. Anyways, my itemisetion is pretty good, and I know how to play Ekko very well so I don't think you'll lose anything from reading this guide, hope it helps! :D
NOTE: This guide is Work In Progress, I work on it every day and update it every patch, so stay tuned for changes, item explanations, tips, tricks, combos, runes/masteries explanations, Teamfighting, Video guides, Images Etc...

+. +.Pros: + Very mobile + Early power spikes + High base damage + Amazing playmaker + Good trading in lane + Easy to farm with + Extreamly fun to play + Area of effect 1.75sec stun

Spacespace

Spacespace

Spacespace

+ +Cons: - Hard to master - Take a lot of poke vs ranged match-ups - Often banned - Doesn't allow you to blink O^O

SUNFIRE CAPE
You have swag as ekko, so sometimes you wanna finish off a kill by just standing next to the enemy champion :D but if they flash away you get mad so you PHASE DIVE INTO THEIR FACE :^)
On a more serious note tho, the raw stats Sunfire gives are perfect but the passive is what makes it so strong, You deal 25 + your current level as magic damage, and since it's so easy to stick to targets with Ekko thanks to the amount of CC, Dash+Blink (Even though he clearly sais NOT to blink) The damage is there throughout the entire fight.

ICEBORN GAUNTLET
Mana, A bit of armor and extra damage + slow, all for 2700 gold? do you need much explaining? Well let's just say your PHASE DIVE procs it, so you slow them as soon as you get in a fight, follow it up with Timewinder and your passive proc + Parallel Convergence stun and you are basically unkitable.

SPIRIT VISAGE
Now as well as the Magic resist, CDR, Health Regen and Health which are all stats Ekko loves, he also benefits a lot from the SPIRIT VISAGE passive, All healing includes both GRASP OF THE UNDYING and CHRONOBREAK. Not much else to say about this item, except that it's extremely cost efficient.

THE DARK SEAL
This item gives you all the stats you want, Which are: Mana, AP, And extra healing from potions which applies to your Corrupting Potion all for only 350G, This item is one of the most cost efficient item in the game in my opinion and absolutely necessary on Ekko. If you are EXTREMELY fed (Like 7/0 by 20 minutes) and you have 2 tank items complete + Iceborn Gauntlet you can upgrade it to Mejai's Soulstealer but note this is risky, if you decide to buy it, go with a little bit of a safer playstyle untill you get more tank stats, but don't forget you are still front line and you still need to initiate, just keep in mind how hard you go for kills.

Laning with Ekko is pretty simple, it's easy to farm thanks to Z-Drive Resonance and Parallel Convergence passive, easy to win trades and in some matchups easy to get free damage off.

Trading
1. Throw out your Timewinder, if it hits your target try to angle the return to hit your opponent as well, then use Phase Dive on them and it will proc Z-Drive Resonance your passive, give you 50-80% movement speed and 30-60% slow so you just run away and hardly anyone can catch up, even not Yasuo dashing through creeps.

2. If you are laning vs someone that you're doomed to take damage from when trading, even if you run, this is the more reliable combo: Phase Dive on them, only then throw out your Timewinder, auto attack, and start running back. The reason for the auto attack in the end is because 1st of all it will most likely proc Grasp Of The Undying and 2nd it will proc Z-Drive Resonance so you can back off faster, but don't forget to angle your Timewinder to hit on the way back.

3. Another combo is the simplest, you throw out Timewinder, instantly Phase Dive on your target, auto attack to proc your Z-Drive Resonance and Grasp Of The Undying, start backing off and angle the Timewinder to hit on the way back.

4. Walk into fog of war, cast your Parallel Convergence to cut off their escape path, walk back and Phase Dive on them to proc the Stun, follow up with Timewinder and a basic attack (This will proc Z-Drive Resonance and Grasp Of The Undying). This combo will let you get free damage off and the next trade will be in your advantage from the very begging of it.

Tips and tricks

1. Once you are level 6 you can use your Chronobreak to get back to lane in a moment, just back, hover over the items you want to buy, you have 4 seconds to press R as soon as you backed.
CONS TO USING THIS TRICK:
A. If it's pre 20 minutes and you are low on mana and hp, you will not have enough time to regenerate any of those stats.
B. You don't have a rewind and a heal so you have to play safe and only farm (unless you're 5/0 and the enemy champ is boosted as fk) or it's a boring lane (vs Malphite for example).
PROS TO USING THIS TRICK
A. You save your Teleport so you can make more plays on the map to snowball the game.
B. It's SO satisfying to do, you need to try it to understand.