Reached the boss Battle 2 times.
Fortunately the game is a cicle, so after doing this 3 times and each being the same here's how it goes.
The jungle can be divided into 4 mayor sections.
-Running
-Shooting
-Quadbike (or whatever those are called)
-Wall Climbing.
To reach the boss one time you will have to go through
Running-Shooting (1 Segment)-Running-Bike-Running-Shooting (2 segments)-Running-Wall Climbing-Running-Boss
So for the 2nd time you will have to do:
Running-Shooting 3 Segments)-Running-Bike-Running-Shooting (4 segments)-Running-Wall Climbing-Running-Boss
The second run won't be much harder than the first one except for a couple new traps that may appear and that in the shooting segments from 3 foward you will be facing orange enemies that throw molotov's at you and deal a LOT more damage.
It is worth noticing that, even though I reached this point several times, the boss DID NOT appear until I was hunting for the Dinosaur skull relic