Lugia seizure is a revamped, animated Crystal sprite made by Pope. However, it's set at an extremely fast frame rate, which makes it look like its having a seizure of some sort. This is mostly derived from the rapidly moving fingers/wings and thrashing of the head and tail. The Lugia Seizure has also been animated in a drawing by lil_umbreon, which also features the sporadic movements of the original.
Member Theories about Lugia Seizure
Some members had observed that the Lugia Seizure looks like it is attempting to text or type while having a seizure of some sort. It is a possibility that the Lugia became mentally unstable after spending its long life in an underwater cave, constantly hearing nothing but the sounds of waterfalls behind it. Either way, it is widely accepted that this particular Lugia is not entirely sane.