Not bashing your idea or riot, but this is something i doubt they'd do
They're not that daring
Also they just nerfed the minions to increase agression, so i dont see this idea coming into play anytime soon....

If it would fix the jungle it would be worth it.

well here's the problem... picture you take out 2-3 champs late game... you ping madly DOBARONNOWLOLOLOL

So your team is doing baron, and suddenly, your little half-baron comes stumbling along. Suddenly, you're fighting Baronx1.5 Suddenly the other team can 3v5 you, ace you, and win the game right there.

Another side note: Riot before has said before something to the extent that too much randomness in a game detracts from its skill requirements. The better players get punished because lesser players could luck out and gain huge benefits. Having a random roaming minibaron adds a HUGE random factor.

tl;dr This is never going to happen, and you need to put a little more thought into suggestions like this..

No, Just no, First of no champ can solo baron at level 6, So if you are trying to deter (keep away) people from the river that is not good becuase it makes ganking hard and the play alot more bland, Also Riot is going for alot more aggressive play style and not being able to gank early does not help then at all

the problem is walking back with 10 hp then boom a river monster pops out *dead*

Well lets say 1/4 baron then! The power ratio is always up for debate! Besides the fact that it has a spawn cycle much like baron but 1/4 of its power makes getting baron more of a team effort! Plus it would not show up and attack unless you are IN THE RIVER FOR A CERTAIN PERIOD OF TIME! The time it takes for a low level movement speed would take for instance! 4 to 6 complete seconds! Along with the fact that it will show itself giving you time to get out of the river before it attacks! Say you are being chased you could be in the river long enough for river monster to show then when you leave the river it'll be attacking your enemy instead of YOU! GEEZ people is it so hard for you to grasp this concept? Also each concurrent bush patch will restart your time in the river! Can't be that hard to veil yourself and use the full aspects of the game!

there should be a river monster hidden in one of the river brushes. then when you walk in it gives you surprise butt ***. afterwards you are slowed for 10 minutes

also note that it has not ****ing way to patrol from 1 half of the river to the otehr without running through mid

How about an invisible gollum somewhere on the map who drops a ring, quite obviously. That ring must be brought to a secret randomly placed cloaked chest which it unlocks. Inside the chest is a map showing the location of the river monster that spawns when the map is picked up. The monster drops a leash which you need to fill with energy from a destroyed inhibitor. When it's charged you can use it to take control of all your minions.
Just imagine having a veigar run into a bush and runs into 500 minions waiting to gank him.

Which also makes me want Riot to add a gamemode for 6v6 where one player got control of all minions once they are passed the last tower on that specific lane and the minions can't actually leave the individual lane's area.