From the Super Mario Wiki
Bowser Stunners are an Amp-like obstacle that first appear in New Super Mario Bros. U. They return in New Super Luigi U and New Super Mario Bros. U Deluxe. As their name implies, they resemble Bowser's head.
New Super Mario Bros. U
In New Super Mario Bros. U, Bowser Stunners make their only appearance in Red-Hot Elevator Ride as obstacles, where they electrocute the player upon contact. Unlike common Amps, Bowser Stunners have special chains connected to another Bowser Stunner, creating a stream of electricity to travel on the chains.
New Super Luigi U
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