Ill stick my theory in here, I have never been involved in the discussion of teased champs before so I will most likely be wrong but this is what I think is going to happen.
There are currently 3 posters out. In each poster the creature seems to get bigger, stronger (less cowardly) and overall just more evolved. I do know that Riot have been wanting to implement a champ with a permanent pet, like Annie and Tibbers but more, well, permanent. So my rough guess to this champion is a Hunter with a persistent pet that will run away under certain circumstances.
If i was to get really spontaneous here then i'd say that every 6 levels, the pet will grow increasing his own and Klebs overall stats. The posters all depict different states of the little - fairly big - HUGE creature, this leads me to believe that whenever the creature changes or evolves that it will gain a new skill set or something along those lines. Like in the first poster it says "river battle runner, runs all the time" So if i was to guess id say the first version of the pet would make you have an ult involving it becoming a mount then running in a straight line or something like that.
Another skill that has more or less been confirmed by the Brush teaser is some kind of trap, this leads me back to my statement when I say the pet would run away under certain circumstances, I believe that whenever you ult and do the run thing then the pet will run away and you need to go place traps around in an attempt to capture it so that you can ult again.
This gets far-fetched now, but who cares right? It's all hypothetical! As I believe the creature caught in the trap will be klebs persistent pent, this leads me to think that one of klebs skills will be to heal his pet, because what use is a pet thats got a bear trap around his ankle when its a pet that is supposed to be running all the time?
Well that's just my theory! Please comment saying your own, you never know but riot might see one of our ideas then decide to adjust it because they like it!
First poster:
https://www.google.co.uk/search?q=all+kled+posters&rlz=1C1VFKB_enGB646GB646&espv=2&biw=1920&bih=955&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjV4_TI8oHOAhWsAMAKHYNXAkgQ_AUIBigB#imgrc=dhjpR20BgT9yYM%3A
Second poster (translated):
https://www.google.co.uk/search?q=all+kled+posters&rlz=1C1VFKB_enGB646GB646&espv=2&biw=1920&bih=955&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjV4_TI8oHOAhWsAMAKHYNXAkgQ_AUIBigB#imgrc=HrLJuMe1AOcRWM%3A
Third poster (translated):
https://www.google.co.uk/search?q=all+kled+posters&rlz=1C1VFKB_enGB646GB646&espv=2&biw=1920&bih=955&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjV4_TI8oHOAhWsAMAKHYNXAkgQ_AUIBigB#imgrc=GtVu40PNzIz6dM%3A