Sergeant Guy Cannon
From the Super Mario Wiki
The Sergeant Guy Cannon is a Banzai Bill Cannon used by Sergeant Guy during Mario's battle against the Elite Trio in Mario & Luigi: Dream Team. Its role in battle is to have a Banzai Bill loaded into it by Sergeant Guy to shoot at Mario the following turn. If Mario does not attack the cannon, the Banzai Bill fires and pursues Mario, the player has to repeatedly press the button to escape the Banzai Bill. If Mario attacks the cannon before it can fire, the Banzai Bill explodes, causing massive damage to the Elite Trio and the active horde of Sub-Goombas.