Crimson Moon Co-op & Crossplay: Confirmed by the Devs

The short answers

What co-op changes

Per the support article, bringing a second Nephilim “isn’t just an extra sword”:

• Shared lives — both players draw from one pool of revives.
• Resurrection — you can revive a downed partner; the Templar Revive Boon gives +50% damage resistance while doing it.
• Synergies — combined abilities “unavailable to a solo player”; Weapon Arts like Angelic Bulwark and Boons like Guardian Angel and Zeal of the Faithful explicitly affect “you and allies”.
• Dynamic scaling — enemy composition and difficulty adjust to party size.

The Slay Together achievement (finish a mission in co-op) had been earned by 32.4% of Steam players one day after launch.

How to start a session

Everything is done from the invite button, held down, at the top-left of the screen — or at the portal in Sanctus Clypeus where matchmaking lives.

• Host: Host Game → choose Private (friends / code only) or Public (matchmaking). You receive a session code you can hand to anyone.
• Invite a friend: host a Private game → open the friends list (the smiley face) → pick an online friend who owns the game → Invite.
• Quick Match: joins an active public session after a short wait.
• Join via code: Join Via Code → enter the host’s code → Submit.

A Steam forum thread reports the game not remembering a session set to Private between launches; it is not on the official Known Issues list.

Crossplay: confirmed, and where it was said

ProbablyMonsters has confirmed crossplay twice, both times on video rather than in a store listing or blog post — which is why it is so hard to find in a web search:

• Developer AMA #1 (the game director answering community questions, YouTube): “It’ll have cross play, yes. We support cross play.”
• Developer AMA #4 (YouTube), on matchmaking at launch: “You can do either a quick match feature or you can join directly by a code … and we do support cross-platform play so you can connect with people from any of the platforms that we’re supporting.”

The supported platforms are the launch platforms: PC (Steam and Epic), PlayStation 5 and Xbox Series X|S. The store pages line up with that — the Xbox Store lists Xbox cross-platform multiplayer and Xbox cross-platform co-op, the PlayStation Store lists online play for up to two players (PS Plus required), and the ProbablyMonsters Account links all four storefronts to one identity so “progress and entitlements follow you”. Steam’s page carries no Cross-Platform Multiplayer tag, but the developer statement overrides the missing label.

What is still not documented: whether crossplay can be switched off, and whether joining across platforms uses the session code only or also the platform friends list. The support article describes the friends list as your platform friends, so the safe assumption for cross-platform play is host a Private game and share the session code.

The co-op progression problem

Two things overlap here. The official Known Issues list says “mission progress may not always be correctly awarded to the host during co-op play”. The top-voted Steam review describes the opposite direction: the joining player’s run did not advance (“they can only start on Mission 1”), and loot is not instanced — one chest, one set of drops. Whether the guest-progress behaviour is a bug or the intended host-owns-the-run model has not been stated. Until it is, the safe assumption is that the host’s campaign is the one that advances, so alternate hosting if you both want to progress.

Other co-op bugs on the official list: an incorrect “Player has left the session” message, clients freezing or disconnecting in Moore Manor, and invitations that leave the joiner stuck on the title screen. A “Consistent connection loss in co-op” thread on the Steam forums matches the second item. Fixes are slated for Hotfix 1.0.1.

Related

• Sanctus Clypeus hub — where the portal and matchmaking sit.
• Platforms — PS5, Xbox, Epic, Steam Deck, Game Pass and Switch 2 status.
• Known issues and fixes