First time playing after S6 changes

I played one game and it felt like URF; everything was hectic.

Kha'zix seems good but it feels like he takes a little more skill to play now because I can't just instantly kill isolated targets with W > E > Hydra > Q > AA it seems, and I actually have to use my ult to juke spells and wait on cds. Not to mention the things I'm trying to assassinate do a ton of damage now so most of my assassinations rely on my ult which I guess isnt too bad because it's a lot easier to get 40% cdr now (unless I'm building him wrong)

So yeah, basically urf

But my biggest concern is the keystone mastery I was using. I don't remember what is was called but it was the DoT one. I went to finish off a yorick with a Q and flashed away expecting the DoT to finish him off (he was around 20 health I believe) and there were no people nearby to use heal but he didn't die? Am I understanding this keystone correctly? Is there like a cooldown or something on it? Are there indicators in place to show if a mastery is doing something like a trail of blood or something to show the dot?

Also any tips on kha'zix for the new season would be appreciated!