"Apophis" refers both to the Egyptian god who embodied chaos and to the near-Earth asteroid (99942 Apophis) discovered in 2004.
The reason for this name is tied to Gastly's chaotic shiny factor, which should result in g8 stars but doesn't do so in practice.
He is a xor8 shiny caught by botting LGPE's GO Park at 13865 encounters after missing one at 7738.
Gen 6+ PIDs with a xor value of 0-15 indicate that the Pokémon is shiny. 0 is square and 1-15 is star.
The way GO Park generates shinies makes the xor value 1-15 15/65536 of the time and 0 65521/65536 of the time.
It's like rolling another shiny on an existing one. Double shiny!
However, the gen 8 games have an override to always display GO shinies as square.
If not for that, this would be the equivalent of an overworld star shiny
His unusual sparkle is masked for now.