Bill Blaster Turret
From the Super Mario Wiki
Bill Blaster Turrets are special Bill Blasters that appear in New Super Mario Bros., New Super Mario Bros. Wii, New Super Mario Bros. 2, New Super Mario Bros. U, and New Super Luigi U. They are essentially multiple Bill Blasters stacked as a pillar, but their cannons periodically rotate and fire in a predictable manner. Unlike standard Bill Blasters, they will still fire if Mario, Luigi, Blue Toad, or Yellow Toad stands adjacent to one of the cannons.
At minimum, they contain two active cannons. Each adjacent space is also aimed in the opposite direction.