This is a build I thought of just for fun, but has some serious potential to destroy squishies. This build gives Kha'zix some huge power by working around his current flaws, namely his q. Since evolving his q no longer grants additional damage when not isolated it is not the focus of this build. This build revolves around multiple items and kha's passive in combination with thunderlord's decree.

When kha attacks with his passive up it counts for two ticks towards the thunderlord's proc. Using his E to get close before attacking allows his passive buffed attack to proc thunderlord's immediately. Now this is where this build gets fun, and a surprising amount of damage follows too. Building triforce and rfc add huge damage to this combo. Around 450 total at level 18 before resistances are taken into effect. Now add the actual auto attack along with thunderlord's, his passive and hydra active and you have got some serious damage. With the core items complete you will have 50% crit which gives the possibility of even more damage. Since all this damage is coming from your E and your items it leaves you with plenty of damage to finish the job and get your reset.

First of all kha has a very rough time in lane, especially in the current meta. Despite this he still has the potential to win lane if your opponent is not ranged and has a hard time poking kha down. If you can hold out and play safe he transitions very well into mid game when you get his core items. From here this build starts to roll some heads. Since your Q will not be your main source of burst damage Kha can pick of carries quickly regardless of where their allies are. Although it's always best to aim for opportunities where enemies are isolated it is no longer essential. What is essential is waiting for your items to be ready and to have your passive and thunderlord's up. Because of this its good to linger on the edges of the fight and jump in to pick of squishies. If you jump in and go balls deep you will most likely be hard cced and die instantly with ought doing anything worthwhile. It is very important to know when to go in and how to escape easily. If you kill someone your ult and E will make this very easy. This build also has a surprising amount of sustained damage. The increased attack speed and life steal increases your survive-ability. The 50% crit chance works well with higher attack speed + life steal and Death's Dance/Maw of Malmortius help to boost your survive-ability too. The high amount of cdr from the build also helps alot by making your q are more consistent damage source instead of a 1 off high damage burst (which it still can be!)

This build is still a work in progress and I will do some more testing to find the optimal build path and runes/masteries. It started as just something for fun but after a couple games I was surprised by the amount of damage you can do. I really like Kha'zix and I hope this build can bring some life back to him after being left in the dust for so long.