Here is my 100% Achievement Guide!
This is for completing the level for riding across the swamp.
To make things a lot easier, destroy the pike, using dynamite and placing it on the tree that is blocking your path.
With that, you not only get an achievement for killing it, but no pikes show up aftwr this one, so you only have to worry about the platforming sections
Go to 35:00 in my video to see exactly where this is done and to see the start
Hope This helps!