In the last level start by jumping on the fire place and collecting
all the ammo(if the flamethrower gets you fall on the ground and roll).
then proceed to the poodle destroying all the tan troopers that are in 
your way(dont shoot the poodle as it's off ammo and you can't destroy
it). Then follow the carpet to the bazooka guy's and destroy them all 
(wath out for the mortar shots). rush to the portall and stand behind 
the portall. Shoot the two thin superweapons and wait. 
The fat superweapon will try to corner and squish you run out of the
other side ,stand behind the super weapon and shoot him in the back.
Walk up to the portal and you won.