User blog comment:Purebreaker/Dawn, The Shadow Assassin/@comment-9939438-20130830011436

Guaranteed crits are a fickle thing...the only other guaranteed crit mechanic I can remember being on an actual LoL champ is Ashe's passive, and even that is very limited. Being able to proc a guaranteed crit AND your opponent won't be able to see you before hand? Plus you can get that cooldown down to 15 seconds, which may mean only using it once per teamfight, but it still seems like it'd be wildly overpowered.

Also, while I'm mentioning the E, I noticed it has no synergy with the passive. Changing that might help remedy the crit situation too. Otherwise, like your ideas.