What I mean by that, is an assassin that doesn't just look for an opening and blows someone up, I mean an assassin who, if skilled enough, is impossible to escape from. The closest example of this is 
, but this is only VIA his ultimate.
They can follow your every step until they find you recalling alone, then proceed to assassinate that target.
...I could possibly see 
given this role, but it would take a bunch of experimenting.
Nidalee is a tracker type, even has traps that reveal players. Rengar is as well, with his bola and brush passive. Warwick has a blood scent (sounds pretty tracker-y to me) and speed boost that makes him hard to get away from without a lot of cc.
lore wise you're describing WW and if you build WW with onhit/AD his ult can do about 1.8k damage that you can follow up with steong AAs and blood scent will keep you on them if they flash after the ult, though he'll blow up if anyone bursty catches him with his ult down, but now that i think about it that's exactly what an assasin does.
Don't they have Head Hunter skins for multiple champs. :P
People already complain about assassins, do you really want the forum to be flooded with crying of kids?
Vayne's Passive. Good luck getting away.
