MARVEL Cosmic Invasion Castle Doom Guide: How to Beat Doctor Doom

MARVEL Cosmic Invasion just got a lot more dangerous. The Siege of Castle Doom, the beat 'em up's second paid DLC from Tribute Games and Dotemu, went live on November 10 and drops you straight into Victor von Doom's own stronghold. Two new heroes join the 17-character roster, and a brand-new roguelite mode asks you to fight your way to Doom before his machine finishes charging. Here's what Castle Doom actually asks of you, and how to come out the other side with your gear intact.

01What Is the Castle Doom Mode?

Castle Doom is a run-based mode built on top of the main MARVEL Cosmic Invasion campaign, not a replacement for it. Instead of a fixed stage order, you pick a path through Castle Doomstadt's branching corridors, fighting through Doom Bots and returning bosses from the base game along the way. The goal stated in Dotemu's own patch notes is simple to say and hard to do: stop Victor von Doom before he can activate his Cosmic Inductor. Succeed and you walk away with permanent unlocks. Fail, and the run ends on the spot — though you still keep some of what you earned.

Unlike the main campaign's set stages, every Castle Doom attempt reshuffles which doors, enemies and rewards you're offered, so no two runs play out quite the same way. That's by design: Tribute Games built the mode around "near infinite replayability," and the branching-path structure is the mechanism that delivers it.

02How to Start a Run and What to Expect

The Siege of Castle Doom unlocks the mode from the main menu once the DLC is installed — you don't need to finish the base campaign first, though knowing the game's combat basics (parries, specials, team-up assists) matters a lot more here than in Arcade Mode. A run begins at the gates of Castle Doomstadt and ends one of three ways: you reach and beat Doom, the Siege Gauge fills before you get there, or your team is wiped by whatever's guarding the next door.

• Pick a hero whose kit you already know well. Castle Doom punishes slow learning curves far more than the campaign does.
• Expect branching doors at nearly every junction, each flagged with the kind of challenge or reward waiting behind it.
• Treat every early fight as a resource check, not just a combat check — you're collecting Battery Cells, not just clearing rooms.

How to Clear a Castle Doom Run

1. 1Choose a hero whose combos and specials you already know. Castle Doom punishes learning a kit mid-run far more than Arcade Mode does.1 min
2. 2Every branching door flags the challenge or reward waiting behind it. Weigh the risk against your current health and Siege Gauge before committing.Varies
3. 3Every hit you take speeds up the Siege Gauge, so treat chip damage as lost time, not just lost health.Ongoing
4. 4Defeated enemies drop Battery Cells, which charge the Stabilizer. Don't skip optional fights that offer easy cells.Ongoing
5. 5Charging the Stabilizer unlocks a perk pick from 12 options plus the next area. Prioritize defensive and tactical perks early, damage perks once you're surviving comfortably.~1 min per pick
6. 6Use team-up assists to clear adds quickly rather than trading hits solo, especially against bosses recycled from the main campaign.Varies
7. 7The run ends instantly if the Siege Gauge completely fills before you reach Doom at the Cosmic Inductor.Varies
8. 8Win or lose, the energy and cells you collected carry over to permanent unlocks and new modifiers for future runs.Instant

03Meet the New Heroes: Invisible Woman and Doctor Doom

Susan Storm joins as The Invisible Woman, described by Dotemu as wielding "fantastic light-bending powers" — the closest the Fantastic Four has to a true support-and-control kit in this roster. Doctor Doom himself is also playable, blending "high-powered technology and occult abilities" into a moveset that, fittingly, is built to punish the very mistakes his castle is designed to cause. Neither hero's full frame-data or combo routes have been broken down officially yet, so treat specific matchup claims you see elsewhere as unconfirmed until you've tested them yourself.

Both heroes are usable in the main campaign too, not just Castle Doom, so it's worth a few Arcade Mode runs to learn their basic strings before committing to them in a timed roguelite run where mistakes cost you the whole attempt.

04Managing the Siege Gauge

The Siege Gauge is Castle Doom's clock, and it's the single biggest thing that separates this mode from the rest of the game. It fills gradually just from time passing, and it fills faster every time your heroes take a hit. As it climbs, the castle's Doom Bots and enemies get faster and hit harder — the run actively gets more dangerous the longer you take. Let it fill completely and the attempt is over before you ever reach Doom.

In practice, that means two things matter more here than in a normal arcade clear: taking as little chip damage as possible, and not lingering in rooms once they're cleared. Blocking and parrying aren't optional defensive flavor in Castle Doom — every hit you eat is time you're taking off the clock. If you're playing with a team, calling in assist characters to clear adds quickly, rather than trading blows solo, keeps the gauge from creeping up during drawn-out fights.

05Choosing Your Path, Perks and the Stabilizer

Every door you choose in Castle Doomstadt offers a different flavor of challenge and reward, and reading those flags before committing is the main skill expression in the mode. Battery Cells you earn from defeating enemies charge the Stabilizer, Reed Richards' invention and your only real counter to Doom's plan. Charge it enough and you can spend it on one of 12 perks spanning defense, damage and tactical upgrades — and charging it fully also unlocks the next area of the castle, so it does double duty as both your upgrade currency and your key to moving forward.

Failed challenges along the way can debuff your heroes rather than simply doing nothing, so a door promising a big reward isn't automatically worth the risk if your run is already shaky. Early on, prioritize defensive and tactical perks that reduce incoming damage or slow the Siege Gauge's climb; damage perks matter more once you're confident you can survive long enough to use them. If you've already explored a different kind of weapon or build overhaul in another live-service shooter, the same instinct applies here — rank your options before you commit resources to them rather than grabbing whatever's offered first.

06Doom Bots, Returning Bosses and the Final Showdown

Castle Doom doesn't invent an entirely new enemy roster from scratch — alongside new Doom Bots built specifically for the mode, you'll run into bosses and enemies pulled straight from the original MARVEL Cosmic Invasion campaign, reused as mid-run gauntlets. If you've already learned a boss's tells from Arcade Mode or the story, that knowledge carries over directly, which is one more reason to treat the base campaign as prep work rather than something you can skip.

The run builds toward Victor von Doom himself, guarding the Cosmic Inductor at the heart of Doomstadt. Nothing official has detailed his exact moveset or attack phases yet, so don't take third-party "safe timing windows" at face value until you've confirmed them in a real run — this is a fight the community is still mapping out. What is confirmed is the stakes: beat him before the Siege Gauge fills, and every hero who lands the final blow unlocks a new color palette as a permanent reward.

07Rewards at Reed's Lab and What to Run Next

Whether a run ends in victory or defeat, the energy and Battery Cells you banked carry over to Reed's Lab, where they unlock new permanent equipment, lab events and modifiers. Those modifiers raise the difficulty of future Castle Doom runs in exchange for better rewards, which is the mode's long-term progression loop — you're not just replaying the same gauntlet, you're opting into harder versions of it once the basic route stops being a threat.

If you're picking up The Siege of Castle Doom at launch, it's worth knowing the DLC also folds in everything from the first expansion: Cyclops and The Thing are both usable inside Castle Doom runs too, giving you 19 total heroes to pull from across the whole game. Mixing a hero you've mastered from the base roster with one of the four DLC additions is a reasonable way to balance familiarity against trying something new.

MARVEL Cosmic Invasion | DLC 2 | New Game Mode Trailer, released October 26, 2026 on Dotemu's official YouTube channel.

Prepare to face the wrath of Doom!💥 The Invisible Woman, Doctor Doom and an all-new game mode await in MARVEL Cosmic Invasion: The Siege of Castle Doom DLC, out now!

— Dotemu (@Dotemu) on X

The Siege of Castle Doom is available now for $7.99 on Steam, Switch, Switch 2, PlayStation 4 and 5, and Xbox Series X|S, with a 10% launch discount running through November 17. Whatever platform you're on, the core loop is the same: learn the castle's threats a little at a time, bank what you can at Reed's Lab, and chip away at Doom's run until the Cosmic Inductor stays dark for good.