How to get fire demon

[Ken Kaneli]

i cant get fire demon when i complete game with orange knight! HELP ME

[^t(rainbow) LuciaBehemoth]

When you beat the game with the Orange Knight, do you have the white skull just above the characters head on the character select screen?

If the white skull is missing you might have accidentally skipped a level when you were playing online. The game inherits the progress of other people, so if you have levels:
A B C
and you've played A but not B or C yet, another person could load you straight into C and the previous level never gets completed!

Please go back through the map and see if any levels feel unfamiliar with you. This guide should help:
http://castlewiki.castlecrashers.com/Levels

Then, beat that level, and re-beat the boss. The character and Insane Mode should unlock for you.