Thanks! The plan was to have the enemies stack up on each others' shoulders too (like the guns), or form cheerleader-style-pyramids and other goofy formations. But we didn't have the time to work that whole system out. This would have made the gun-stacking a more useful mechanic, as the higher your stack the taller "enemy tower" you could defeat.
The bigger enemies and the blob "amalgamate" monster thing were a sort of compromise to add some variety within the 48 hr limit.