Mortal Shell II is getting into the Halloween spirit. Rotten Autumn is a free seasonal update from developer Cold Symmetry and publisher Mortal Shell 2. It went live on October 20th, 2026, two months after the game launched in August. It comes with a roughly one-minute launch trailer that moves quickly through new cosmetics, a photo mode, an alternative soundtrack, new dungeons, and a few holiday jokes, including a pumpkin worn as a helmet.
Quick answer: Rotten Autumn is free and live now on Steam, PS5, and Xbox Series X|S. Update Mortal Shell II and the new dungeons, Tarstones, Shades, photo mode, and soundtrack are ready to use.
Mortal Shell II Rotten Autumn update contents
The trailer shows most of the update but skips a few smaller items. Here is the full list, grouped by what each addition does in the game.
| Addition | Type | In the trailer? |
|---|---|---|
| 15 New Dungeons | Content | Yes |
| 10 New Tarstones | Items | Yes |
| Sheep Specific Tarstone | Item | Implied |
| All New Shell Shades for Each Shell | Cosmetic | Yes |
| Harbinger Pumpkin Helmet | Seasonal cosmetic | Yes |
| Impervious Lute skin and lute tracks | Seasonal cosmetic | Yes |
| Alternative soundtrack by Sakis Tolis | Audio | Yes |
| Photo Mode | Feature | Yes |
| Overkill Graphics Settings | Graphics | Yes |
| New Lighting Presets for Nightmode | Graphics | No |
| Ghost of a lost Shell | Seasonal event | No |
| Polish and bug fixes | Maintenance | No |
On Steam, the update arrived as build 26073152. It came just three days after the patch released on October 17th.
15 new dungeons and 10 new Tarstones
In Mortal Shell II you play as the Harbinger, who possesses fallen warriors called Shells. The world already had more than 60 dungeons at launch. Rotten Autumn adds 15 more, which is about a 25 percent increase in that kind of content. In the trailer, the dungeon section opens on a statue holding two curved blades in a room full of candles. It then cuts to fast clips of spiral staircases, floating stone platforms, traps, and fights in glowing arenas.
Combat works the same way it did at launch. Mortal Shell II has no stamina meter, so fights focus on chaining attacks and breaking enemy posture. The new dungeons do not change that system. They give you more places to use it.
The trailer shows the 10 new Tarstones as a row of icons under a warrior kneeling at a candlelit shrine. One of them is a Sheep Specific Tarstone. A white sheep also walks across a circular floor toward a warrior in the trailer. Cold Symmetry’s update notes end with a joke denial that there is a sheep dungeon, despite whatever you may have heard.
Photo Mode and Overkill Graphics settings
Mortal Shell II launched without a photo mode. Rotten Autumn adds one. The trailer freezes a fight in mid-swing to show the menu, which includes these controls:
- Camera: Free Camera, Orbit Mode, Center Drone, Drone Up and Drone Down
- Framing: Field of View (75 by default), Camera Roll, Constrain Aspect Ratio, Toggle Grid
- Output: Screenshot Size (1x shown), Take Shot
- Look: Presets such as “Sieler’s Embrace,” Brightness, Volumetric Scattering
- Scene: Game Speed, Pause Game, Clear UI, Hide All, Reset All
Overkill Graphics adds a distinct graphics-settings tier beyond the options already available. It appears beside photo mode, though it isn’t restricted to screenshots. The update also brings new Nightmode lighting presets that alter the game’s look after dark, but the trailer doesn’t show them.
New Shell Shades and the Harbinger Pumpkin Helmet
Shell Shades are cosmetic outfits for the game’s Shells, and every Shell gets a new one in Rotten Autumn. The trailer runs through them quickly. There is spiked armor, horned mystic robes, gilded plate, red assassin robes, a black-and-gold scholar outfit, and heavy knight armor.
The Harbinger Pumpkin Helmet is the seasonal cosmetic. It shows up more than anything else in the trailer. A bare-chested fighter with a glowing carved pumpkin for a head swings a two-handed sword. In the last shot, that same pumpkin-headed fighter kneels on an empty plain while a huge spiked, horned beast rises out of the ground.
Sakis Tolis soundtrack and the Impervious Lute
Sakis Tolis, frontman of the Greek black metal band Rotting Christ, composed an alternative soundtrack for the game. It is an extra option, not a replacement for the original score. The trailer introduces it with two characters playing stringed instruments next to carved pumpkins, with heavy metal playing over the scene.
The Impervious Lute is a cosmetic skin for the lute, which is already in the game. It comes with additional lute tracks to play. The trailer shows the lute up close next to candles, then shows a hooded figure playing it beside a campfire.
The trailer does not show the last seasonal addition. The ghost of a lost Shell now wanders the world and leaves cryptic notes for players who find it.
Rotten Autumn platforms and price
Rotten Autumn costs nothing for anyone who owns Mortal Shell II. It is out on PS5, Xbox Series X|S, and PC through the Mortal Shell II Steam page. The trailer ends with the Mortal Shell 2 and Cold Symmetry logos and the line “FREE UPDATE OUT NOW.” Once your copy has updated, you can open photo mode, select the new soundtrack, and equip the new Shades and the pumpkin helmet. The new dungeons are spread across the game’s existing world.
Cold Symmetry says more is coming after Rotten Autumn but has not given a date for the next update. For now, this October patch adds a good amount of new content for players who have already finished the game, and it gives new players a pumpkin to wear.
