So, the concept behind this build is CDR and Burst!! Let me break it down for you!
Ekko has a 3-hit passive that does magic dmg when proc'ed, this build like to build onto that.

First the Gunblade! This is the bread and butter of the build, while you have just the revolver, your AA's on Champs does extra magic dmg on a 30 sec cooldown! But when upgraded, it ZAPS the target for ALOT and i mean ALOT of Magic dmg and slows them by 40% for 2 seconds. Combined with Thunderlord's and the rest of the build and you will see the true potential shine through!!

Second, the Lichbane!! This puts the SLAM in Ekko Slam!! We all know and love Sheen, for those who dont, Sheen gives extra physical dmg on your next basic attack after using an ability, which is on a 1.5 second cooldown and has 10% CDR!! This is insane on Ekko because Ekko's 'E' ability has 2 parts; First, the dash in a targeted direction, And second an extended range BASIC ATTACK that teleports you to your target! The key word there is... Basic attack, this means that by activating the first part of your 'E', you activate Sheen. And by hitting your target, you consume the extra dmg from Sheen. This is a butt tonne of extra dmg no one ever expects!!

Next is Zhonya's!! This is really self-explanatory. If you need to get out of a sticky situation and by your self a few more precious moments, use this!! This is great! Say you tower dive your laner and kill them, you can Zhonya under turret and reset the aggro on your minions, or just to give you a few moments on your cooldowns so you can 'E' out of there!! A great item that will save you time and time again!! Also has that juicy 10% CDR

Next lets talk boots! Lucidity boots gives you that last bit of CDR you need to cap it off at 45%!! There are other boot options suck as Ninja Tabi's and Merc Treads for all your resistances, but with max CDR on Ekko you can jump around and destroy your opponents before they can cry for their mummy's!!

To top the whole build off, you grab some BIG AP items suck as Rabadon's Deathcap and Luden's Echo to make you more deadly than before, and sneak in a Void Staff if they decide to build MR against you!!

To roll all this info into a deadly package, you would through your 'Q' out and get 2 stacks of passive on the target, then you would 'E' towards them and teleport to them while simultaneously activating Gunblade!! This will; Comsume your passive stacks and inflict EXTRA dmg, also comsume Sheen proc for EXTRA dmg, while also SLAMing then with the 'E' dmg as well, and to top it all off, i nice juicy Gunblade active to the face... This equates to ALOT OF DMG!!

This dmg in the late game is HUGE!!, just using 'E' and consuming Sheen will be above 500 dmg, keep in mind that this combo of 'Q' and then 'E' combo while consuming passive stacks is on a 5 second cooldown, and the 'E' with Sheen dmg is on a 1.5 second cooldown!! Then you put it all together, with the passive stacks and Gunblade dmg on top of that, which easily exceeds over 1000 dmg on a 40 second cooldown!!

Thats all that i have for you guys!! Try the build and let me know how you go!!

Thanks a lot for reading and i hope you enjoy SLAMing your opponents into an alternate reality!!