I'm making opposite bandnames, here's what I came up with so far...
Arch Enemy would be Best Friend
In Flames would be Out of Water
Nightwish would be Daydespise
Helloween would be Christmes
Iron Maiden would be Wooden Butler
Guns N Roses would be Swords N Flowers
Metallica would be Woodico
Black Sabbath would be White Monday
Norther would be Souther
Wintersun would be Summermoon
Sonata Arctica would be Caprice Antarctica
Children Of Bodom would be Parents Of Lake
Dark Tranquility would be Bright Loudness
Symphony X would be Orchestra Y
Nevermore would be Foreverless
Alestorm would be Coffeecalm
Slayer would be Pussy
Strapping Young Lad would be Unstrapping Old Man