Information found online is most likely outdated. All information is to be changed following theory debunk streams, upcoming Patreon comics, and the pilot.
Arackniss is Angel Dust's brother and is currently planned to appear later on in the story. According to a sketch Vivienne Medrano did once, Arackniss was the one that killed Angel and apparently gave him a black eye before doing it, however this is not canon. It is also speculated that his real name is Jackson, however, this may or may not be canon. Another speculation is that he had hung himself, and influenced Angel's death. Though, this is more than likely un-canon within the series. According to Arackniss's original design, he was supposed to be a cyclops with 7 other eyes surrounding it. His design was changed for unknown reasons.*
*Revision & sources are severely needed.