It's like Jekyll & Hyde!!!!111! The fantasy band has to mesh though, you can't put Trey Spruance and Mike Patton in the same band or something IT JUST WON'T WORK THEY WON'T MESH. They have to mesh.
The nightmare band can't be Chickenfoot because they already exist. HOWEVER you could say "Chickenfoot with Peter Criss on drums" and that would be allowed. That works for the fantasy band too. Like "Kyuss but with Dio singing".