Although it is part of the Imperial Dalek faction, this dalek is more of an outcast even than the baseline daleks that are contending with the Imperial Dalek faction.
The main weapon of this particular special weapons dalek is the plasma weapon that can destroy all other known opponents. It is a fixed weapon so that this dalek can only fire at targets straight in front of it. The radiation generated by this weapon is also fairly intense and no-one is entirely sure what this has done to the dalek creature inside the casing, though it's undoubtedly nothing good. The power of it's weapon also has a lot to do with the untidy paintwork.