Use a clone Maxwell to spook the guard (Maxwell will also take the gun from the guard).
The guard should run to down to the middle floor, then put the cloned Maxwell back down with him. Maxwell should drop the gun, also make sure you don't get rid of the clone yet, keep him and the guard towards the left wall in the middle floor, the clone may steal your gun if close enough.
Now the guard is out of the way, go to the middle floor and use the gun to destroy the tiki and the small crate.
Use shrinking magic on yourself and go to the bottom floor.