Effects are additions to the knife the player has equipped, and sometimes modify the corpses based on the effect. Most of the effects were fixed when the March 2020 Update came out. They are not tradable. Below is a near complete list of each one.
| Effects | |||
|---|---|---|---|
| Name | Knife/Kill Effects | How to Obtain | Image |
| Pumpkin (2017) | Small Pumpkins appear on the knife | Halloween Event 2017 (Expired) | 
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| Radioactive | Surrounds the knife with a green glow and turns the Victims bodies Green | Buy in the Shop | 
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| Musical | Musical Notes appear out of the knife - No death effect | Buy in the Shop | 
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| Doge | Small Doge Icons appear on the knife and turns Victims into a Doge | Buy in the Shop (Expired) | 
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| Darkfire | Gives the knife a Black Fire Effect and burns the Victims with it | Buy the Shadow Item Pack (Expired) | 
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| Heartify | Pink Hearts appear out the knife and turns Victims eyes into Hearts | Buy in the Shop | 
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| Flaming Knife | Puts a Fire Effect on the knife and burns the Victims with it | Buy in the Shop | 
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| Elite-ify | Small Black Skulls appear out the knife and Turns the Victims into a Flaming Red Skeleton | Buying the Elite Gamepass | 
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| Blue Flaming Knife | Puts a Blue Fire Effect on the knife and burns the Victims with it | Buy in the Shop | 
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| Pink Flaming Knife | Puts a Pink Fire Effect on the knife and burns the Victims with it | Buy in the Shop | 
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| Green Flaming Knife | Puts a Green Fire Effect on the knife and burns the Victims with it | Buy in the Shop | 
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| Rainbow Flaming Knife | Puts a Rainbow Fire Effect on the knife and Burns the Victims with it | Buying Murder Mystery 2 Merchandise (Expired) | 
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| Snowflakes (2016) | Surrounds the knife with Snowflakes | Christmas Event 2016 (Expired) | 
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| Dual Wield | The Player holds 2 knives instead of 1 | Buy in the Shop | 
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| Electric Knife | Surrounds the knife with electricity, turning the Victims into Skeletons and making a Buzzing Sound | Buy in the Shop | 
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| Easter Glow | Surrounds the knife with a pink and blue glow | Easter Event 2023 (Expired) | 
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| Flow | Gives the knife a blue glow and surrounds the victim's corpse with blue smoke and bubbles | Buying the Summer bundle fromSummer Event 2023 | 
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| Floral | Gives the knife a purple glow with cyan flowers | Summer Event 2023 | 
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| Knifeception | Small Dependent Knife Clones appear out of the knife | Buy in the Shop | 
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| Bats | Surrounds the Knife with Bat Particles | Buying the Halloween Item Pack (Expired) | 
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| Monify | Covers and surrounds the Victims Corpse into Money | Buy in the Shop (Expired) | 
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| Gearstorm | Turns the Victims into Gear Parts | Buying the Clockwork Item Pack (Expired) | 
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| Bitsplosion | Turns the Victims into Small Colorful "Bits" | Buying the 8-Bit Item Pack (Expired) | 
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| Ghostify | Makes the knife translucent while ghost particles appear out of the knife and turns the Victims into Ghosts | Buy in the Shop | 
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| Blizzard | Gives the knife some Icicle Particles | Christmas Event 2017 (Expired) | 
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| Candy Cane Effect | Small Candy Canes appear out of the knife | Christmas Event 2017 (Expired) | 
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| Snowflakes 2017 | Small Snowflakes appear out of the knife | Christmas Event 2017 (Expired) | 
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| Northern Lights | Gives the knife a Blue, Green and Pink Glow | Christmas Event 2018 (Expired) | 
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| Gingerbread | Small Gingerbread-men appear out of the knife | Christmas Event 2017 (Expired) | 
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| Common Ornament | Small White Ornaments appear out of the knife | Christmas Event 2018 (Expired) | 
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| Uncommon Ornament | Small Blue Ornaments appear out of the knife | Christmas Event 2018 (Expired) | 
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| Rare Ornament | Small Green Ornaments appear out of the knife | Christmas Event 2018 (Expired) | 
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| Legendary Ornament | Small Red Ornaments appear out of the knife | Christmas Event 2018 (Expired) | 
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| Knife Wrapper | Wraps and surrounds the knife in Green Christmas Wrapping Paper | Christmas Event 2017 (Expired) | 
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| Ethereal | Surrounds the knife in Foggy Blue Smoke | Buying the Ghostly Item Pack (Expired) | 
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| Poison | Surrounds the knife in Green Smoke and has "Poison" dripping from it | Halloween Event 2019 (Expired) | 
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| Candies (2019) | Small Candies appear out of the knife | Halloween Event 2019 (Expired) | 
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| Frostbite | Surrounds the knife in a "Frost" manner | Buying the Frostbite Item Pack (Expired) | 
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| Vampire | Surrounds the knife in a Red Glow with Blood Particles | Buying the Vampire Item Pack (Expired) | 
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| Batswarm | A Slight Black Glow will surround the knife while Bats appear out of it | Halloween Event 2020 (Expired) | 
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| Hallow's Blaze | Surrounds the knife in an Orange Glow | Halloween Event 2020 (Expired) | 
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| Snowfall | Gives the knife a White Aura with Snow Falling to the Bottom of the Knife | Christmas Event 2020 (Expired) | 
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| Frostfire | Gives the knife a Blue Glow Effect | Christmas Event 2020 (Expired) | 
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| Jingle | Surrounds the knife in a Yellow, Green, and Red Glow | Christmas Event 2020 (Expired) | 
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| Ghosts (2020) | Surrounds the knife with ghostly particles and Fog | Halloween Event 2020 (Expired) | 
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| Phantom | Green Ghouls and fog will surround the knife | Halloween Event 2021 (Expired) | 
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| Wraithfire | Surrounds the knife in a Purple Glow | Halloween Event 2021 (Expired) | 
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| Snowflake | Surrounds the knife in a White Glow while Snowflakes appear out of it | Christmas Event 2021 (Expired) | 
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| Starry | Surrounds the knife in a Yellow Glow while Stars appear out of it | Christmas Event 2021 (Expired) | 
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| Aurora | Green, Blue, and Purple Glowing lines will surround the knife | Christmas Event 2021 (Expired) | 
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| Ice Magic | Surrounds the knife in a Cyan, Purple, and Pink Glow | Buying the Ice Bundle (Expired) | 
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| Plasma | Sparks of Blue and Purple Plasma surround the knife | Buying the Plasma Bundle (Expired) | 
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| Ghostly | Ghost-like teal and blue flare surrounds the knife | Buying the Ghost Bundle (Expired) | 
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| Versus | Surrounds the knife with swift-moving icons of the Zombie and Survivor teams | Halloween Event 2022 (Expired) | 
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| Candies (2022) | Drops candies of green, blue and orange. | Halloween Event 2022 (Expired) | 
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| Pumpkin (2022) | Surrounds the knife with orange fog and disembodied faces of a pumpkin | Halloween Event 2022 (Expired) | 
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| Toxic | Surrounds the knife with green smoke and green bubbles | Halloween Event 2022 (Expired) | 
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| Void | Surrounds the knife in dark purple smoke with black particles | Redeem Roblox’s Murder Mystery Crown hat through Amazon Prime Gaming (Expired) | 
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| Petals | Surrounds the knife in petals and turns Victims black with pink petals emitted | Buying the Sakura Bundle Gamepass for 3,399 robux (Expired) | 
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| Rainbow | Surrounds the knife in rainbows and puts a rainbow effect over the Victims with it | Buying the Rainbow Bundle Gamepass for 3,399 robux (Expired) | 
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| Darkswirl | Surrounds the knife with a black aura and emits a black fog from the Victims body. | Buying the Darkness Bundle Gamepass for 3,399 robux. (Expired) | 
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| Ghosts (2023) | Surrounds the knife with small cartoon-ish ghosts. | Halloween Event 2023. (Expired) | 
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| Candies (2023) | Red, orange and yellow candies fall from the knife | Halloween Event 2023. (Expired) | 
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| Glowy | Blue glowy circles, as well as 3 colored pumpkins are emitted from the knife. | Halloween Event 2023. (Expired) | 
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| Traveler's Flame | Surrounds the knife with bright orange flames. | Halloween Event 2023. (Expired) | 
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| Swirls | Tiny peppermint candies of white, red, and green. | Christmas Event 2023. (Expired) | 
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| Stars | Surrounded by a faint yellow aura with glowing star outlines twinkling around the knife. Has a death effect. | Christmas Event 2023. (Expired) | 
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| Fireworks | Surrounded by a faint aura of red, green, blue, and pink, with popping fireworks of different shapes and sizes. Has a death effect. | Christmas Event 2023. (Expired) | 
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| Flowerwood (Effect) | Similar to Flow, a blue aura appears around the knife which emits a blue aura around the corpse of a dead player along with cyan particles. | Easter Event 2024. |  |
| Flowers (Effect) | It has a faint white aura along with white daisy flowers and white petals, hence the name. | Easter Event 2024. |  |
| Matrix | It gives the knife a green, spiky aura along with lime green rectangles and squares. | Easter Event 2024. |  |