only for him to realize its a
with 

Accurate.
"Bippity boppity, your ass is now my property."
[sg-janna]
Love that wagging tail in the back
Fixed it. giphy>imgur.
But how do they know it's not the 12/2
who has her ult up.
but u say not like those save her if he has enough items but she'll usually have them when shes done with her damage items but i think i worded my first comment wrong which led to your misunderstanding. what i meant is like a
with
sure this might seem like a terrible build but when we get rid of her ga she just goes into her
or
. and this is a full on late game duel. sure rengar WILL dominate kaisa early and maybe mid depending on how strong the kaisa and rengar are but kaisa just has such a strong late game and rengar falls off (not saying he loses alot of 1v1s because he sure as hell can still beat people) but in teamfights rengar just dosent have a place late game aside from catching out isolated prey and the moment rengar jumps on kaisa she'll more than likely be in a lane and she should only be in the jungle if shes trying to prevent a baron or drake to be taken or getting jg camps and that sweet sweet red buff that all adc players like to take at 20 mins. in a jungle fight if rengar jumps to kaisa in a spot where kaisa can easily just press e and reposition herself in a better spot to kite him in and when he runs to the bush he'll more than likely be marked and kaisa will w and proceed with her ult and get that barrier to finish rengar off. Ive played this matchup MANY TIMES and only a few times i beat the kaisa because rengar just gets kited by her so easily without bushes and when i flash on her she just ults to reposition.