For mutators you need to set the variable of each mutator like the following in your command line:
Mutator="MutatorCommand1","MutatorCommand2","MutatorCommand3"
| NAME | MUTATORS |
| Bonus Combos | BonusPack.MutCrateCombo |
| BigWheels | Onslaught.MutBigWheels |
| Lightweight Vehicles | Onslaught.MutLightweightVehicles |
| Onslaught Weapons | Onslaught.MutOnslaughtWeapons |
| Stunt Vehicles | Onslaught.MutWheeledVehicleStunts |
| Vehicle Arena | OnslaughtFull.MutVehicleArena |
| UT Classic | UTClassic.MutUTClassic |
| Lightning Guns | UTClassic.MutUseLightning |
| Sniper Rifles | UTClassic.MutUseSniper |
| UTV2004S | UTV2004s.utvMutator |
| Super Berserk | UnrealGame.MutBerserk |
| BigHead | UnrealGame.MutBigHead |
| Game Speed | UnrealGame.MutGameSpeed |
| LowGrav | UnrealGame.MutLowGrav |
| Air Control | UnrealGame.MutMovementModifier |
| UT2003 Style | XGame.MutFastWeapSwitch |
| InstaGib | XGame.MutInstaGib |
| No Adrenaline | XGame.MutNoAdrenaline |
| QuadJump | XGame.MutQuadJump |
| Regeneration | XGame.MutRegen |
| Slow Motion Corpses | XGame.MutSlomoDeath |
| Species Statistics | XGame.MutSpeciesStats |
| UDamage Reward | XGame.MutUDamageReward |
| Vampire | XGame.MutVampire |
| Zoom InstaGib | XGame.MutZoomInstagib |
| Arena | XWeapons.MutArena |
| No SuperWeapons | XWeapons.MutNoSuperWeapon |
| Bonus pack Vehicles | OnslaughtBP.MutBonusVehicles |