B: Recurring Nightmare: Pyramid Head will thrust the Great Knife forward. If it hits, the victim will be pinned for a moment while a clone appears to the side of, behind, or beneath them. The clone will materialize with a spear and stab them. May be charged.
(For Kirby, the clone will instead be Bandana Waddle Dee.)
B-Up: Rust Form: Pyramid Head flakes apart and dissolves into rust before the particles reappear and reform his body a short distance above. Anyone that touches the particles takes trivial damage, but is affected by a 'corruption' DoT. Trajectory may be slightly manipulated.
B-Down: Hellscape: Pyramid Head postures slightly the convulses and an aura of rust surrounds him. Anyone that touches the aura will be afflicted with corruption, and any part of the stage it touches will develop a pool of corruption (causing things to appear 'rusted') that spreads for a couple of seconds before dissipating.
B-Forward: Impale: Pyramid Head manifests his spear in his free hand and throws it forward, impaling any characters it hits. Piercing attack that can hit multiple opponents. (Partially inspired by the Javelin Toss in New International Track & Field)
Final Smash: Misty Day - Time of the Judgement
Pyramid Head manifests his spear, raises it, and slams it down in an arc before him. If anyone is caught by it, the screen fades and the character's face fades back in, upside down. The camera pans out to reveal them suspended in a rusty cube above an alter in a heavy fog with darkness all around. As they begin to panic, a Pyramid Head approaches from each side wielding a spear pointed downward. They tap the spear on the ground, flip it to point upward, and then simultaneously impale the victim as the screen goes to a silhouette and fades to black.
Stage-wise, I'd say Carroll Street, in front of Brookhaven Hospital. The edges of the stage would be places where the street is broken off leading into an abyss, as seen in the games, and periodically an airhorn will sound converting the stage to and from the rusted, alternate version of Silent Hill.