Why Carnage Is Strong?

Carnage (Cletus Kasady): The original human host of Venom's spawn was the sociopathic serial killer named Cletus Kasady. Kasady's insatiable bloodlust bestowed the symbiote with power surpassing those of its progenitor, making Kasady much stronger than Venom and Spider-Man combined.

Why is carnage so powerful?

Originating as an offspring of Venom, Carnage is much more powerful than their parent symbiote because of the symbiotes' biology, and is in many ways a darker version of him.

How does Carnage get his power?

Carnage was once a serial killer known as Cletus Kasady, and became Carnage after merging with the offspring of the alien symbiote called Venom during a prison breakout. The symbiote amplified his psychotic nature making him even less mentally stable than he had been previously, and therefore even more dangerous.