Why did they give Rengar a guaranteed crit?

Because they are two separate champions that don't have much relation. Taking crit of off one champion doesn't mean anything for whether or not to give crit to another.

So I don't know why Rengar got a crit, but it has nothing to do with Shaco.

A better question is why did they give him 30% free bonus AD (42% of Kha'zix gets killed)?

That's a bigger problem with his kit.

I think they should make Rengar's ult-hop just a regular damage boost rather than a crit. It adds too much to his burst. Literally every other assassin has had a significant delay on their burst. Fizz - 2s, Akali - 2s, Kat - situational daggers, Talon - .75s W and R.

Why does Rengar get special treatment and have a R>Hop>Q 1 shot? He can keep his damage if he wants, just delay it a bit more. The fact that as soon as I see Rengar pop out of his ultimate my screen turns gray is an indication that they failed to open up his burst window, which was the whole purpose of the assassin rework. He's 1 shotting faster than before. The only difference now is that you have to be grouped 24/7 from the pure threat of his 49s ultimate alone that also lasts like 15s.

Again, the problem is his Bonetooth necklace.

First they need to fix that, and then we can look into whether or not his other abilities are truly overpowered or if it was just Bonetooth that made them as such.