Catatonic Schizophrenia: This is the most likely diagnosis, as malignant catatonia is often associated with schizophrenia, particularly the catatonic subtype. The symptoms of catatonia, such as immobility, mutism, and rigidity, are characteristic of this condition.

Bipolar Disorder with Catatonic Features: Bipolar disorder can also present with catatonic features, and malignant catatonia can be a complication of this condition.
Major Depressive Disorder with Catatonic Features: Catatonia can also occur in the context of major depressive disorder, and malignant catatonia can be a severe manifestation of this condition.
Neuroleptic Malignant Syndrome (NMS): NMS is a life-threatening condition that can be induced by neuroleptic medications, and it shares many symptoms with malignant catatonia, such as rigidity, fever, and autonomic instability.

Encephalitis: Encephalitis, particularly autoimmune encephalitis, can present with catatonic symptoms and must be ruled out due to its potential for severe consequences if left untreated.
Status Epilepticus: Non-convulsive status epilepticus can manifest with catatonic symptoms, and it requires immediate recognition and treatment to prevent long-term brain damage.
Septic Encephalopathy: Sepsis can cause encephalopathy, which can present with catatonic symptoms, and it is essential to identify and treat the underlying infection promptly.

Lethal Catatonia: This is a rare and severe form of catatonia that can be fatal if not recognized and treated promptly.
Anti-NMDA Receptor Encephalitis: This is a rare autoimmune disorder that can present with catatonic symptoms, and it requires specific treatment with immunotherapy.
Wilson's Disease: This is a rare genetic disorder that can cause neurological symptoms, including catatonia, and it requires prompt recognition and treatment to prevent long-term damage.