General synonyms:
* Aggressive
* Brutal
* Fierce
* Forceful
* Intense
* Savage
* Vicious
* Wild
More specific synonyms:
* Bloody (referring to bloodshed)
* Ruthless (lack of mercy)
* Destructive (causing damage)
* Ferocious (wild and aggressive)
* Hostile (unfriendly and aggressive)
* Savage (cruel and brutal)
* Unbridled (lack of control)
Synonyms emphasizing the intensity:
* Extreme
* Overpowering
* Rampant
* Unrestrained
The best synonym to use will depend on the specific context of the sentence.