YOU, again? Achievement
Defeat the Humanoid Tank Mk1.*MISSABLE*
When you get to the forest area, at the first junction you'll find a scavenger sitting down against a pole. Head down the right path toward Area B to find this boss encounter. There are multiple ways through the forest, so you could skirt this on accident. If you get to Area F (where you'll head south to find the rebel hideout), head north instead to run directly into this battle. Going to the rebel hideout first is actually a good idea, since you can heal and save there prior to the fight.