The Toxic Blaster is like a laser gun to kill the monsters in Steamworks Island. Put it on to your mech and hit the space bar to attack.
How to get Toxic Blaster
And now we finally learn the secret of what happened to all the inhabitants of Steamworks Island. If you will talk to the citizen they will ask you to fight the monsters using the toxic blaster. Jump up to the platforms on the right and get the Toxic Blaster. Then get back in your Mech and attach it.