In addition to the Warstructs that wreaked havoc in the days of old, there was also a much more dangerous threat in the form of Knightmares, servants of the diabolical Darkrai who were far more unpredictable, not to mention sinister. Created by Darkrai injecting his essence into the corpses of fallen soldiers laid to rest in Cresselia's Realm of Sleep, the Knightmares were an absolute terror both in the physical world and the Dreamworld. That was, until Cresselia got wind of her husband's schemes and sealed the Knightmares into an annexed portion of the Dreamworld... yet even from there, the Knightmares found ways to terrorize the living for millennia.

Each Knightmare embodied a particular phobia, and oftentimes their actions involved making that associated fear a reality, which in turn grants them power. They are also a perversion/inversion of their original species' characteristics. Ghast here is the embodiment of the fear of loss, more specifically "loss of a loved one". Many a time he would personally murder a target in order to throw the deceased's loved ones into despair and hysteric grief, after which he would kill them, too. It's how he got those Cubone skulls adorning his outfit--after all, he has no sympathy or remorse for orphans, or children in general, really.

In the present day, Ghast and his fellow Knightmares--Two-Hands, Knightmare of Silence (Ambipom) and Sinthia, Knightmare of the Flesh (Mandibuzz)--used their power from within the Dreamworld to cause an accident in Unova's Dreamyard Laboratories, which set the whole facility ablaze. The accident was caused as a way of claiming as many victims as possible--researchers, patients, and even the Rescue Workers who had arrived on the scene, one of whom was a then-3-year-old Hamilton's father, Cameron Koa Blakewood, who was ultimately caught in an "explosion" that made a large portion of the Dreamyard mysteriously vanish....