The bulk update request #8223 has been approved by @Hillside_Moose.
create alias arachnemon -> archnemon
create alias arukenimon -> archnemon
While to be mythologically accurate the character's name should be Arachnemon, officially it's pronounced and spelled as Archnemon (see Wikimon). Arukenimon is the romaji reading and the spelling the dub went with.