Not to be confused with Silas.
Sil'as Dahcsnu is a member of the Dagon'hai order. He can be found in the Tunnel of Chaos. He has no purpose during the quest, but his talk options end up with him questioning your magical powers, and he will then cast a spell on you. If your Magic level is below 80, will cause your character to dance and shout, "Argh! I can't stop dancing/headbanging/jumping!" However, if you have level 80 Magic or higher it will backfire onto him, making him dance instead. This is a requirement to complete the Elite section of the Varrock achievements.
The spell cast by Sil'as Dahcsnu working on a lower-level player
The spell cast by Sil'as Dahcsnu backfiring