Kha' Zix, but is he really that unseen ?

I mean, his passive states he's an 'Unseen Threat', but the fact that I'm in lane 24/7 and that my enemy has vision on me seems to show that I am a threat, just not that unseen.
So here's my suggestion :

####Unseen Threat

When Kha'Zix is not visible to the enemy team, he gains Unseen Threat. Unseen Threat causes his next basic attack against an enemy champion to deal bonus magic damage and slow by 25% for 2 seconds.

Unseen Threat lasts 3/4/5/6 seconds (depending on his R) or until consumed and the damage is increased against isolated targets (if you have Q skilled).

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The damage could be nerfed a bit to make it balanced again.