Doom is Necrobinder's signature kill threshold. If Doom reaches or exceeds current HP, the target dies at the end of the turn.
Mega Crit gave Doom one of the clearest mechanical definitions in the sequel. Doom is applied similarly to Poison, but it does not tick down and it does not deal damage over time.
Instead, a target dies at the end of the turn if its Doom total is equal to or greater than its current HP. That single sentence is why Doom deserves its own page rather than being buried inside a generic Necrobinder guide.
Verification note
Based on Mega Crit's October 16, 2025 Necrobinder reveal. The public explanation is precise enough for a clear first-pass rules page.
Why Doom matters
If you are seeing Doom for the first time, start with the rule. That is the fastest way to make sense of the fights, cards, and choices built around it.
Once the basic rule clicks, the related links show you where Doom starts changing real decisions in a run.
Learn the rule before you worry about ranking or build theory.
Open the related guides if Doom changes pathing, card picks, or early-act risk.
Come back after major updates if wording, balance, or examples change.
The official reveal is careful here. Doom is not a slow poison clone. It is a threshold mechanic that sits on an enemy until the number is high enough to convert into an instant kill check.
That means players have to think in breakpoints. If you can reduce HP and raise Doom in the same turn cycle, the payoff can be dramatic. If you cannot, Doom may be a setup burden before it becomes a win condition.
Because Doom checks current HP rather than maximum HP, the mechanic naturally rewards decks that can manage both sides of the equation. Lowering HP efficiently makes every point of Doom worth more, while stacking Doom without pressure can be too slow.
That is why the best launch-week Necrobinder advice is to think in mixed damage plans rather than in a fake binary between Doom and normal combat.
Lead with the threshold rule, then add examples and edge cases as players discover them. Many sites will waste time calling Doom 'like Poison but stronger'; the official wording is already better than that shortcut.
Comparison
Doom is not a lightly renamed old keyword. It introduces a threshold-kill identity that the launch roster of the first game did not have.
Slay the Spire 1
The original launch classes did not build around a class keyword like Doom that turns low-enough enemies into immediate kills.
Slay the Spire 2
Necrobinder uses Doom as one of the class's defining mechanics.
Why it matters
Returning players need a new damage math instinct for Necrobinder runs.
Slay the Spire 1
Damage planning usually focused on whether you could block, burst, or scale fast enough.
Slay the Spire 2
Doom adds a second question: when can you set up the threshold kill cleanly?
Why it matters
It changes lethal planning from pure output math into setup timing.
More mechanics pages
FAQ
No. Mega Crit explicitly says Doom is applied like Poison, but unlike Poison it does not tick down and it does not deal damage over time.
At the end of the turn, if the Doom number is at least as high as the target's current HP.
The official reveal presents Doom as part of Necrobinder's identity. Until the live card pool proves otherwise, that is the safest way to describe it.
Sources
Mega Crit early access launch post
OfficialOfficial launch article for the current early access build.
Mega Crit release date trailer post
OfficialOfficial summary of the launch date, the five-character roster, and co-op support.
Neowsletter: Necrobinder and Doom
OfficialOfficial explanation of Osty, Doom, Souls, and card transformation.