Co-op runs up to four players, and the front door is tighter than most groups expect. The host has to be Steam friends with everyone joining. There is no matchmaking, and no password lobby you can post in a Discord. Local co-op is not supported. If the people you want to play with are not already on your friends list, sort that out before you plan an evening around it.
Everything past that gate is more interesting than a straight port of the solo game. Threats are shared. Resources are not. That one split is what makes co-op play differently, and you want it clear before your first fight rather than during it.
Setting up a lobby
Load the right save profile before anyone touches Multiplayer. Every player has three profiles, and unlocks live on the profile rather than the account. A fresh profile has only the entity:ironclad. Spin one up for the occasion and you will find your character roster gone.
With profiles sorted, the order is short: choose Multiplayer from the main menu, one player hosts, everyone else joins, then each player picks a character. Duplicates are allowed. Four Ironclads is a legal party, and given the profile rule above, sometimes the only party a new group can field.
| Lobby rule | Detail |
|---|---|
| Party size | Up to 4, one host plus three joiners |
| How you connect | Steam friends only, joined from the main menu |
| Matchmaking | None |
| Private lobbies | No password option |
| Local co-op | Not supported |
| Character picks | Duplicates allowed |
How a co-op fight differs
Enemy stats scale and change with the size of your party, and enemy attacks hit the entire party. Your Energy stays your own; nothing is pooled. You can spend it at any point during the party's turn, and the turn only advances once every player has selected End Turn.
That pairing matters more than it sounds. There is no lock-in step, so cards land as they are played and the party can act in sequence. Let the damage go first, look at what survived, then decide who spends on block. Sequencing this way costs nothing and converts a lot of near-lethal turns into clean ones. The cost of a shared End Turn is that the slowest player sets the pace of every fight, which is fine on Act 1 elites and grating by the third boss.
Because attacks come in at the whole party while Energy stays private, defense does not concentrate. Every player answers party-wide damage out of their own hand, so a deck with no block is a group problem rather than a personal one. Take the defensive card sometimes even when your curve is screaming for the attack.
A player who dies is revived after the battle as long as the party wins it. That makes a death mid-fight survivable rather than fatal, and it changes the math on a dying player's last few turns: spending them on damage to close the fight out is often better than spending them on staying alive.
Co-op also brings in multiplayer-specific cards that never appear in a solo run, so the card pool you are drafting from is not the one you have memorized.
Loot, paths, and node behavior
Rewards are private. Every relic, card, item, and coin of gold belongs to the player who took it.
| Node or system | Co-op behavior |
|---|---|
| Path selection | The party agrees on a path, or RNG picks when it cannot |
| Relics, cards, items, gold | Per player, nothing pooled |
| Ancients | Each player gets their own randomized options to pick from |
| Random events | Each player makes their own choice and takes their own outcome |
| Campfire | Gains Mend, which restores 30% of one ally's HP |
| Shop | Different stock and different prices for every player |
| Treasure chest | One reward per player; RNG settles it when two want the same one |
Path selection has no voting system. Nobody's pick outweighs anyone else's, and a three-to-one split does not go three's way. The party either agrees or the game rolls. Settle the route on voice before anyone commits, because a disagreement is not a negotiation the game will arbitrate for you.
Private gold has a knock-on effect worth planning for: nobody can bankroll the party's strongest deck. Four separate economies, four separate shops with their own stock and prices. The player who found the gold-generating relic gets a better shop than everyone else. Campfire Mend is the exception, and one player burning their rest to top up somebody else is frequently the right trade when that somebody is carrying the run.
Save file rules, and the ones that will cost you
This is where groups lose progress, so read the whole table before your first session.
| Rule | What it means in practice |
|---|---|
| One campaign per profile | Each player has three profiles; each profile holds one campaign at a time |
| The host owns the save | The campaign is tied to the host's profile |
| Starting fresh costs the old run | Hosting a new game with a different group abandons the existing save |
| Full roster from turn one | A player cannot be added partway through a campaign |
| Everyone present to continue | Anyone can quit whenever they like, but the campaign only resumes with every original player there |
| No substitutions | A player who drops cannot be replaced mid-campaign |
Read those together and the real rule falls out: a co-op campaign is a commitment by a fixed roster. The seats are assigned at the start and stay assigned. Pick your host on schedule reliability rather than enthusiasm, because their profile is the campaign and their absence is the campaign's absence too.
The awkward case is a friend group of five. You cannot rotate the spare through the fourth seat. That seat belongs to one person for the whole campaign, and the fifth player's only option is a separate campaign hosted by someone else. Three profiles per player is the release valve here, since one person can hold up to three campaigns at once, one per profile. Just do not reuse a profile that is already carrying a run you care about, and remember that a second campaign on a brand-new profile starts you back at the Ironclad with nothing else unlocked.
Multiplayer Ascension and the floor rule
Multiplayer Ascension is a separate track. Whatever you have climbed solo does not carry across; multiplayer starts from scratch no matter how deep your singleplayer ladder runs. Unlocking works the way you already know: clear all three acts, in a team of two to four.
Two details make the climb easier than it first looks. Levels can be earned with different groups, and an unlocked level applies to every character you play in multiplayer. Your Ascension progress belongs to you, not to a particular roster, so you can climb with whoever happens to be online.
Then the catch, and it is the most useful thing to know before your group builds a schedule around co-op: the party plays at the Ascension level of its lowest-unlocked player. Three players sitting at a level the fourth has not unlocked means the whole table drops to the fourth player's level. There is no averaging.
Plan for it. If your group wants to climb, the group climbs together, or the one person who keeps missing sessions becomes the ceiling for everybody. When it does happen, the fix is a clear at the missing level in any team of two to four, which is where the different-groups rule pays off. Two of you can drag the straggler through while the rest sit the night out, and the level sticks to them permanently. One evening spent doing that beats a month of the whole party playing beneath its level.