which prevent you from getting in, or anything else from getting out.Your third grunt starts just north of this Plateau, and really cannot go anywhere unless he picks up that SpongeGun
(or someone else picks it up first
). I'd pick it up, if I were you.There are two enemy gruntz
just within range of your new weapon. Use it on them! Be careful, as you may find yourself within range of the enemy grunt(z) 
where one of your buddiez warped in.Then they will begin to roam around, and may take pot shotz at your buddy as well as you!
Remember the enemy gruntz
? Every chance you get, lob spongez at them. Repeatedly.Until they are no longer within range.
Use 'Hit and Run' tacticz against the enemy grunt
surrounded by Spikez 
and Holez z, until he is a quivering puddle of Goo 
. Then you may concentrate on fewer targetz.Then move so that the Rock-throwerz
are within range again. Soften them up as much as you can.There will come a point at which they are no longer within range from this side of the Plateau.
This is where thingz can begin to "go wrong, go wrong, go wrong". Plan your next movez carefully.
Perhaps a change of scene, until other obstaclez are removed?
Maybe another Grunt is (or will be) better equipped to deal with this area.