Alastor

Alastor's demonic (or "complete") form manifests when he uses his magic to the max, gets angry, or wants to intimidate enemies. At this point, his appearance becomes grotesque, huge, and reminiscent of a creature from nightmares.
Changes in appearance
Height and proportions: His body is highly elongated, becoming unnaturally tall and emaciated. Short limbs and fingers turn into long, bony legs.
Giant antlers: The small deer horns on their heads instantly grow into huge, branchy black antlers.
Radio Eyes: Alastor's eyes are completely transformed. Whites can turn neon red or black, and pupils transform into the glowing dials of old radios, frequency scales, or radioactive hazard signs.
Terrible Maw: His eternal smile expands literally from ear to ear. The lips disappear, revealing huge, razor-sharp, glowing yellow teeth. A dark substance may ooze from the mouth.
Environment and Special Effects
Radio Interference: Radio broadcast symbols, neon hands, dial signs, and static physically materialize around him.
Space Distortion: The reality around Alastor darkens and turns a blood-red hue. The picture around him begins to ripple, like on a broken old TV.
Shadow Tentacles: From its silhouette and from the ground, giant black tentacles and anthropomorphic shadows erupt with the same insane smiles that obey its orders.