First it appears to be a regular Dummy.
However, by loading it up with gear, then hitting it's special "Absorb Mass" ability, it converts whatever is in it's hands into extra mass for itself.
When the mass really begins stacking up, it begins to gain a gravitational field. If it gets more mass, it will begin to absorb items that it comes into contact with, beginning with low-mass items such as bullets or terrain. If it increases more, eventually weapons and actors will be drawn in and devoured.