The Calamitous Devourer can only be achieved if the Devourer’s Calamitous abilities reach critical levels and was shown in the final chapter of the Golden Deceiver but this means that this form can only occur under certain conditions that are very difficult to happen.
Anyways the power of the Calamitous Devourer is below.
The Calamitous Devourer has its infinite Calamitous beam, which was powerful enough to put a hole through the Deceiver’s tough scales easily.
The Calamitous Devourer can also use a much stronger, calamitous burst ability which makes a massive 5 mile wide explosion that eradicates anything in it.
The Calamitous Devourer potentially has more abilities but those need to be discovered, for that to happen, the Calamitous Devourer will have to happen again.