Fusion cannons were massive turrets that guarded barricades leading towards the Hall of Paradoxology (H.O.P.). They did not operate for the Minions, but rather for Dr. Croid. When the heroes used Leon, a reprogrammed Guardian, to reach H.O.P., the cannons rose up from towers aimed at the Guardian, charged up the cannons and released a powerful blast of fusion at the Guardian, causing massive damage. However, when charging the Fusion Cannons, they were vulnerable to attack from the Guardian's guardian cannons located on its back. They were only seen on barricades, often only guarding two, though some guarded four. The Fusion Cannons were some of the few weapons that could punch a hole into a Guardian.