Mutants are piss easy. Mission with lots of mutants? Beat the shit out of thugs before the mission to get super saiyan rage (maybe a weapon). If theres like 5 at once use it and take 3 out.
If its 1v1 mutant use x combos only. he attacks? roll around him. then hit him with 2 LT+Y attacks. hit with x combo again and repeat. Also stay in the gas they spew. It does no damage and fills up the weapon meter. Free asswhoopin juice.