The Mound: Omen of Cthulhu Launches Free The Cult of Tsathoggua Halloween Update on PS5, Xbox Series X|S, and PC With a New Underground Lair and Rank 70 Cap
Following its launch on July 15, the four-player cooperative cosmic horror game The Mound: Omen of Cthulhu is celebrating the spooky season with its biggest content drop to date. Chilean developer ACE Team and publisher Nacon have officially released The Cult of Tsathoggua, a major free update available right now on PlayStation 5, Xbox Series X|S, and PC (Steam) with full crossplay support across all three platforms.
Inspired by H.P. Lovecraft's novella The Mound, the first-person expedition thriller sends squads of explorers deep into a cursed jungle where deteriorating sanity distorts what players see and hear. Alongside the free patch, the base game is currently featured in a Halloween promotion at 35% off on Steam, dropping the price from $39.99 to $25.99, while an optional cosmetic DLC, the Tsathoggua Cultist Skin Pack containing four cult-inspired outfits for the starting explorers, is available for $2.99. Console players looking for even more weekend sessions can also check out the six games included in Xbox Free Play Days through November 1.
The Shrine and Lair of Tsathoggua: Facing a Bulletproof Great Old One
The centerpiece of the Halloween update begins aboard the Galleon, the expedition's hub ship, which has received a seasonal Halloween makeover. Once players have unlocked the southern regions, they can head down to the lower deck and speak with a mysterious chained prisoner to start a brand-new questline: The Shrine of Tsathoggua.
To unlock the new underground territory, crews must locate 6 Eyes of Tsathoggua hidden inside shrines during Treasure Hunt missions, with a limit of one Eye per expedition. Surviving the extraction is mandatory: any Eye lost during a failed run will not count toward progression, though Eyes collected while playing as a guest in another host's lobby are credited to your own save. Once the host brings six Eyes back to the Galleon, the entire four-player squad can descend into Tsathoggua's Lair.
Ruling over this subterranean cavern is Tsathoggua, a colossal amphibian Great Old One that changes the rules of engagement: the entity is completely immune to conventional firearms and standard weapons. Squads cannot rely on black powder to survive; instead, they must scour the dark cavern for torches, salts, and medical supplies while figuring out an alternative method to bring the deity down. The darkness also introduces the Frog-Fishman, a new amphibious threat lurking in the lair and near the Mound, alongside new tentacle hazards during Portal Contracts.
Eye of Servitude, Swivel Breech Flintlock, and High-Risk Cursed Treasures
Defeating Tsathoggua rewards every player in the party with the Eye of Servitude, a powerful occult relic that can be held up toward a monster to turn creatures against their own kind. Back at the Galleon shop, explorers can also equip two new combat tools: the explosive Hand Grenade and the Swivel Breech Flintlock, an upgraded firearm capable of firing two shots before reloading.
Looting shrines has also become far more dangerous with the addition of Cursed Treasures. Signaled by a red inventory flash, an audio cue, and an on-screen warning, each cursed artifact inflicts a severe penalty on whichever crew member carries it back to the ship:
- Screaming Idol: Constantly emits loud cries while carried, drawing unwanted attention across the jungle.
- The Trees Will Listen: Turns nearby trees hostile, causing their branches to lash out at the carrier.
- Mi-Go's Beacon: Summons a Mi-Go directly to the holder's position, with a second one joining the hunt if held too long.
- Blood Price: Cuts the carrier's maximum HP by 50% for as long as the treasure remains in their inventory.
Rank 70 Level Cap, 13-Perk Skill Tree, and Asymmetric Sanity Hallucinations
Beyond new monsters and loot, ACE Team has overhauled character progression by raising the maximum level cap to Rank 70. Players now earn one skill point per rank to spend at the statue aboard the Galleon across a brand-new skill tree, which can be reset for free at any time while keeping bonus inventory slots unlocked at no cost. Whether playing on a desktop rig or on a handheld with the new Xbox Series dashboard plugin for Steam Deck, explorers can specialize their builds with 13 distinct perks:
- Survival & Mobility: Carry Strength (carry bodies without losing movement speed and pick up items faster), Stamina Bonus (boosts stamina to 125% and 150% across two tiers), Bleed Resistance (two tiers of bleeding duration reduction), Red Dust Immunity (prevents worm parasites from breathing red dust), and Dread Damage Resistance.
- Stealth & Navigation: Improved Night Vision (projects a faint glow in total darkness), Map-Savvy (reveals potential item locations on the map), and Armor Specialist (allows silent running while wearing heavy armor).
- Combat & Starting Loadouts: Backstab Specialist (prevents enemies from evading backstabs), Knife Specialist (unbreakable knife), plus Pious, Bomber-man, and First Kit to start every expedition with a crucifix, a bomb, or smelling salts.
Finally, the update expands the game's signature psychological horror with new item hallucinations: as sanity drops, explorers may misperceive the equipment in their hands while their teammates witness something completely different over spatial voice chat.
My Perspective
The Cult of Tsathoggua addresses the exact areas where The Mound: Omen of Cthulhu needed more depth after its July launch: long-term character specialization and high-stakes extraction dilemmas. Cursed Treasures like Blood Price and The Trees Will Listen turn a routine walk back to the Galleon into a tense tactical gamble, especially when one player has to sacrifice half their health bar for the squad's payout. Combined with an underground boss impervious to gunfire and a flexible Rank 70 skill tree, this free Halloween update gives four-player crews plenty of reasons to brave the jungle again.
Based on the outskirts of New York City, Chaya 'Chayane' spent five years studying software engineering in Montreal before returning to her home state. A Full-Stack developer and Deep Learning AI architecture researcher, she explores neural networks and algorithmic optimization while engineering data pipelines for Retrocharting and Gamescharting alongside Grimtag. A gamer for over 20 years and an avid collector of Nintendo history and The Legend of Zelda, she explored World of Warcraft's Azeroth before bringing her deep technical background to video game analysis.
