This Seeking Tech guide will show you how to get the All Paths Less Traveled trophy and achievement in Metal Slug XX.
Unlock Requirements: “Clear all 3 hidden paths.”
Use the following video as a visual aide:
The first path is located close to the red “Danger” explosive barrel in the 1st Mission. Instead of heading to the right, drop down the pitfall in the middle of the screen to get to the hidden path.
The second and third hidden paths are right next to each other. On the fifth mission, playthrough the level normally until you get to the end of the second section. Instead of heading to the right, go left instead to find a hidden pathway.
The end of this pathway has a teleporter that you can take to the second hidden path. If you jump past this teleporter instead and head all the way to the left, then you should find the third hidden path.