A.
(Hes insane, did you expect anything else? Stop licking your damn weapon.) (I find even if it weren't Nasus causing him to freak out, he or Jinx would be fully capable of starting all the fighting with one action.)
B. Any guild so:
+ her team would probably HG style gangbang you until the finals if you weren't too careful.
C.
(Who knew tears were so ineffective?)
C2.
(Anyone that could easily ignite Amumu) (Fire Spreads! Yeah!)
D.
(I'm somewhat a pacifist.)
E.
(Y-Y--You...threw my...blocks.....FUUUUUUUUU-)
F.
(Eh, he even says he has trouble shooting and aiming along with the fact that lore wise hes just a rat with a crossbow.)
G.
(Q FARM Q FARM Q FARM Q FARM Q FARM)
H.
(Satan not dying instantly after Amu, him being invisible is the only way he could actually survive for a while in this situation.)
I.
(Seems strange but if you under-estimate Gnar's capabilities, its gonna suck when you get hit by a building. Gnar's cute factor probably would give him some more times of safety against champions that could be swayed by him, you gotta vote for the underdogs right?) I'd assume everyone knowing of his special ability would either make him a target or a person you would stay away from. So, he could abuse this to keep himself safe for a good amount of time but there is a big possibility he could be easily teamed against in the early rounds due to his power.
I2.
/
(These IMO can be replaced with:
/
/
Nas: Q FARM DEAR JESUS HES ONE SHOTTING OMFAGFASOFAO- Teemo: Just you know, being a dick and setting shrooms to get kills then disappearing as if he were never there to begin with. J4: Probably biggest target aside from those ones from Shurima but he would have a good time knowing Demacians would have trouble attacking him.)
I3. Finalists?: (I explained Gnar) Rengar/Kha are really good hunters and knowing that they possess the abilities to be amazing in the jungle and knowing eventually they would fight each other to the death would make one even stronger. Also, since its a goal to stay safe and be considerably careful in a situation like this you would want to avoid the lonely dark jungle that could easily kill you faster than you could perceive it. This gives them an advantage since they've grown quite accompanied with their surroundings lore wise.
I4. (I myself would find Rengar as the one that would make it to the end since he does possess more landscape advantages and better knowledge of the area around him and since he is a master of hunting he would easily know Kha's weaknesses from their first fight.
J. (WAHGHAHGA SUCH HARD CHOICES, HOW LONG HAVE I BEEN WRITING THIS?!) So, instead of instantly announcing my winner, i'll try to summarize what a battle between the two would be like.
VS
(Why!? Oh btw, I promise i'm not playing the main wins game) So, according to Rioters, Gnar VS Rengar was indeed, a tie, and both easily forgave each other and are staying in a neutral position from each other. I myself feel they would be an interesting match but there are limits: Rengar is a master hunter, hes done it for years and hes nearly died doing it and he will never stop doing it. Gnar -when in Mini form is a normal child, which, like Annie, could boost survival rates if he was opposed by a champion that had humane feelings. Although, Rengar isn't afraid to hunt and would probably keep Gnar/Kha alive because he would want to fight them on his own to prove who is the best hunter like he always wants to do. Gnar possesses the abilities of the child unless enraged, and the fact that Rengar is fully aware of this weakness after being in contact with him could result in an easy victory. So....here it is: The Winner (IMO) would be: 
J1. Why? Easy, Rengar (again) is a master hunter who studies his prey, if he notices one prey gives him a hard time, he will do his best to assert himself as the best hunter. Although, Mega Gnar could have an advantage in power, Rengar has already easily drained Gnar's health if he even survived in time to activate his Mega form. Gnar just doesn't stand a chance compared to him. So...yeah....Kitty Cats practically all that.
(My Though Process: Manly, heroic champs go bye-bye first since they commonly rush into battle, weak exploitable champions usually get betrayed (Amu), and smart ones that want to survive will either play their cards safely or hide until the "heroic" ones destroy each other. Think HG for how I did this)
Edit: Still think I should've swapped Gnar now that I look back at this. Who do you think I should of swapped him with? (No olaf)