Walkthrough (playable in any mode)

Grunt Description of what to do
Bare-handed This Grunt is free to move, so start with him. He will free your other Grunt
Gravity Bootz Go placez no one else can go (painlessly), once you are free to move.
Now just follow his exploitz, until he is stalled, then use someone else.
When you see that horizontal line, it is time to switch Gruntz.