For mutators you need to set the variable of each mutator like the following in your command line:
Mutator="MutatorCommand1","MutatorCommand2","MutatorCommand3"
| NAME | MUTATORS |
| Instagib | UTGame.UTMutator_Instagib |
| BigHead | UTGame.UTMutator_BigHead |
| Low Gravity | UTGame.UTMutator_LowGrav |
| Super Berserk | UTGame.UTMutator_SuperBerserk |
| Friendly Fire | UTGame.UTMutator_FriendlyFire |
| No Translocator | UTGame.UTMutator_NoTranslocator |
| Speed Freak | UTGame.UTMutator_SpeedFreak |
| Handicap | UTGame.UTMutator_Handicap |
| No Powerups | UTGame.UTMutator_NoPowerups |
| Slomo | UTGame.UTMutator_Slomo |
| Weapon Replacement | UTGame.UTMutator_WeaponReplacement |
| Weapon Respawn | UTGame.UTMutator_WeaponsRespawn |