Clarx Ultra is a stronger form of Clarx. He is more powerful then his normal form, or even stronger than Textreme, because he is so powerful that he can destroy Fantendo without even any help.
This form appeared for the first time as a Final Boss. His attack pattern is like Marx Soul's but like Clarx, is faster and at random order. Once defeated, unlike the original counterpart, he send a horrible screech instand of a very noisy scream. He is still alive, despite this monsterous defeat, as prove the True Ending.