So, it finally happened. After years of the community begging, modding, and eventually just using Steam Remote Play to suffer through laggy connections, The Binding of Isaac online game is actually a real thing. But honestly? It’s not exactly what people expected.
If you’ve been out of the loop, you might think this is just a quick patch. It’s not. It’s a massive, free DLC update called Repentance+ that dropped around the 10th anniversary of Rebirth in late 2024. Most people think "online" just means playing with a buddy, but there's a whole lot of weirdness—and some genuinely frustrating bugs—under the hood that you need to know before you risk your 1,000,000% save file.
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The Chaos of Isaac Online: Friend Match vs. Quick Match
The game doesn't just let you invite a friend; it has three distinct ways to play. You’ve got Friend Matches, Public Matches, and Quick Matches.
Public matches are basically a wild west of chaos. You’re jumping in with three strangers who might be literal gods at the game or people who have never seen a tinted rock in their life. It’s a gamble.
One thing that’s super cool—and kinda terrifying—is the Emote Wheel. Since there’s no built-in voice chat, you’re stuck using little icons to tell your teammates "Hey, don't take that experimental treatment!" or "Blow up this wall." It works better than you’d think, but when things get hectic in the Depths, the wheel usually just turns into a spam-fest of crying Isaac faces.
The Revive Machine: A Literal Lifesaver
In the old local co-op, if you died, you became a ghost baby. You were basically a minor annoyance to enemies. In the online mode, Nicalis added Revive Machines.
These things show up in boss rooms. You have to feed them coins—usually 10 for the first go—to bring a teammate back to life. It changes the economy of the game. Do you buy that Soul Heart in the shop, or do you save the 10 cents because your friend is notoriously bad at dodging Mom’s foot?
What Nobody Tells You About the Sync Issues
Let’s get real for a second. The netcode isn't perfect.
Because the game is still technically in an "open beta" phase within the Repentance+ branch, desyncing is a massive headache. If one player lags, the whole room can jitter. In a game where a single frame determines if you get hit by a Brimstone beam, that’s a big deal.
The worst part? Save data corruption. There have been reports of hosts having their save data mixed up with a desynced guest. It's rare, but it happens. If you’re playing this, for the love of God, back up your persistentprogress files. Seriously. Just copy the folder. It takes two seconds and saves you 500 hours of heartache.
The "Sins" System: Who’s Actually Helping?
At the end of a run, the game now gives everyone a "Sin" title. It’s basically a breakdown of how you played.
- Gluttonous: You took hearts while others were dying.
- Greedy: You hoarded all the coins.
- Slothful: You barely killed anything.
It’s a funny way to call out your friends, but it also tracks stats in your main menu. If you’re a "Savior" (reviving people a lot), the game remembers.
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How to Actually Play the Binding of Isaac Online Game
You can’t just launch the game and see a "Play Online" button immediately if you’re on the old version. You have to opt-in.
Currently, on Steam, you need to right-click the game, go to Properties, then Betas. In the past, you needed codes like theyvegonetoplaid or combthedesert. Now, most users can find the Repentance+ branch in the dropdown menu.
- Close the game.
- Go to Steam Library.
- Right-click The Binding of Isaac: Rebirth.
- Select Properties > Betas.
- Select the Repentance+ Beta (or the latest online branch).
- Let the 2GB-ish update download.
A Huge Warning: You have to disable your mods. All of them. Even the "External Item Descriptions" mod that everyone uses. If you don't, the game will either crash or just won't let you join a lobby. The good news is that the online update actually added a built-in version of item descriptions that unlocks after you beat Mom for the first time. It's not as detailed as the mod, but it’s better than nothing.
Balancing the Basement
Edmund McMillen didn't just add multiplayer; he rebalanced a ton of items.
Items that were historically "trash" got massive buffs to make them viable for four-player runs. For example, The Bean and Kidney Bean now work on a 4-second cooldown instead of needing a room clear. Milk! now blocks shots like a shield before it breaks.
They even fixed the Tick. You can finally remove it if you find A Lighter. It only took ten years, but we got there.
The Boss Room Loot Split
In a single-player run, the boss drops one item. In the online game, it drops an item for every player.
However, they share the same pool. If you're playing with four people, the game scales the health of bosses significantly. You aren't just steamrolling through. If three of your teammates are dead and you’re facing Delirium alone, you’re basically fighting a version of him meant for four people. It’s brutal.
Final Verdict: Is it Worth the Hassle?
Honestly, yeah.
Despite the lag and the risk of losing progress, playing a "true" online run is a completely different experience. It feels like a chaotic board game where everyone is yelling at each other about who gets the Polyphemus.
If you want to try it, stick to the Friend Match option first. Playing with people you actually know makes the desync issues easier to manage because you can at least coordinate a restart if things get buggy.
Next Steps for Players:
- Backup Your Saves: Go to
Documents/My Games/Binding of Isaac Repentanceand copy those files elsewhere. - Disable Mods: Don't even try to run them; it'll just break the lobby.
- Learn the Emotes: Practice using the wheel in the starting room so you aren't fumbling with it while a boss is charging at you.
- Check Your Version: Ensure you are on the Repentance+ branch on Steam; the standard game does not have the native online menu yet.