HardHead

HardHead is a virus from the Mega Man Battle Network series. When it is closed, it is invulnerable to attacks. When open, it becomes vulnerable, and it launches cannonballs towards its target. Those cannonballs can break panels. In Mega Man Battle Network 3, HardHead2's cannonball turns the panel it lands on into a lava panel and HardHead3's cannonball leaves the panel it lands on frozen.

HardHead
HardHeads are gray when closed. When open, they become red.

HardHead2/ColdHead
HardHead2s are yellow when closed. When open, they become red.

HardHead3/HotHead
HardHead3s are light-blue when closed. When open, they become red.

HardHeadΩ
HardHeadΩs are forest green when closed. When open, they become blue.