Rubenstein's Monster is a gun that is created when both the RUBE-ADYNE Prototype and the RUBE-ADYNE MK.II are acquired. It rapidly fires pink lasers that can bounce once.
- This gun is not needed for completion. You can unlock the Finished Gun without having this gun's Ammonomicon entry filled.
- Since this gun has no quality, the Resourceful Rat won't give anything in return for it if you trade it with him using the Ring of the Resourceful Rat.
- The fact that the RUBE-ADYNE Prototype and MK.II must be combined together to make a laser rifle is a possible reference to the dual-wield zap guns and the wave gun from Call of Duty: Black Ops' zombies mode, due to the zap guns being two laser pistols that combine together to form the wave gun.
- This synergy makes an appearance in the animated trailer for Advanced Gungeons and Draguns.
- The name of this synergy is a mix of “Frankenstein’s Monster” and “RUBE-ADYNE”.