The Gatekeepers (KH III:DR)

The Gatekeepers were powerful Weapons of War shaped like Giant Armours in Kingdom Hearts III: Darkness Rising, at their smallest they stood at Seven Meters Tall and at their Highest they stood at Fourteen Meters, they were the Super Weapons of the Zarathian Empire during the Keyblade Age that almost brought their Light-aligned enemies to their knees.

Positive Effects
The Gatekeepers are incredibly powerful assets on the Battlefield, they channel the powers of Darkness both within one's heart and of the Dark Realm as their power-sources, without actually harming the heart of their Pactmaker however it is claimed that one either with a balanced Darkness and Light or a Denizen of Darkness fight most effectively with them. Also, the design of the Gatekeepers is much similar to the Keyblades and the Armours on a massive scale, therefore they can do almost all the abilities that Keyblades and Keyblade Wielder Armour do.

Negative Effects
The excessive use of the Gatekeepers (turning on and off) under a short period of time is exhausting and strains on not only the body and heart but also the soul, drawing too much energy from the Realm of Darkness through the use of the Darkness in a person's heart leads to a larger drain on the user, at the end of the day the power-source of the Gatekeepers is ensured through User's life-force feeding drawing Darkness into the Gatekeeper. Despite the fact that diseases, many poisons and viruses don't effect the user in this state, Dinivas the Black Knight does have a unique poison that effects the use of life-force causing the user to become dreadfully ill.