Its in-game description reads "Armband said to have been forged by Satan." Like all armbands of its tier, this brassard is very powerful, it has 3 elementals stats which are at a high level, its Attack power is also good. You'll be able to take down enemies with only few charged projectiles of magic. You can only find the Satan Brassard in dungeons' chests : you can't invent it and you can't buy it in weapons shops. The Satan Brassard is a high-tier weapon (Tier 7) : it'll gain 6 Synthesis Points (SP) per level-up.