Flatten•Attack

Is Flatten good in Slay the Spire 2?

Flatten is a common Necrobinder attack in Slay the Spire 2. In combat it resolves as: Osty deals 12 damage. This card costs 0 -cost if Osty has attacked this turn. It currently underperforms most alternatives, sitting at D tier in our Slay the Spire 2 card rankings.

Across 171 recorded runs, decks running it win 22.0% of the time, comfortably clear of the 18.9% average, by 3.0%. It’s a more selective pick, turning up in just 4.5% of decks that could run it. Necrobinder players keep it in 20.6% of their runs, so it’s a familiar sight in those decks. On average it shows up 1.4 times in the decks that take it.

It performs best next to Debilitate — together they post a +25.1% swing in win rate. It also has strong chemistry with the relic Fragrant Mushroom, which moves its win rate by +23.0%. At 2 energy, it’s upgraded in 23.5% of runs and usually joins the deck around floor 9.

Upgraded, it gains +4 OstyDamage, which is why so many decks invest a rest-site upgrade in it. That’s 33 wins, 117 deaths, and 21 abandoned runs with it in the deck. The encounter that most often ends a run carrying it is Kaiser Crab Boss, which closes out 5.8% of its appearances. Read on for Flatten’s complete synergy, class, and threat breakdown to decide whether it earns a slot in your Necrobinder run.

Best Cards to Pair with Flatten

Ranked by win-rate lift, Flatten performs best alongside Debilitate (+25.1%), Hang (+24.7%), and Mad Science (+23.6%).

Debilitate+25.1%19 runsHang+24.7%17 runsMad Science+23.6%8 runsEnfeebling Touch+19.5%17 runsLegion of Bone+19.3%6 runsGlimpse Beyond+19.3%6 runs

Based on small co-occurring samples — treat these as early signals, not final verdicts.

Flatten Win Rate by Class

Flatten is drafted only by the Necrobinder, where it holds a 22.0% win rate across 171 runs.

The Necrobinderappears in 20.6% of its runs (171 tracked)

Best Relics for Flatten

Flatten pairs best with the relics Fragrant Mushroom (+23.0%), Anchor (+22.4%), and Big Mushroom (+22.3%), ranked by win-rate lift.

Fragrant Mushroom+23.0%6 runsAnchor+22.4%24 runsBig Mushroom+22.3%4 runsFunerary Mask+20.4%8 runsFestive Popper+19.8%13 runsRazor Tooth+19.3%5 runs

Based on small co-occurring samples — treat these as early signals, not final verdicts.

Flatten Card Details

Flatten is a common attack costing 2 energy; it’s upgraded in 23.5% of runs and usually picked up by floor 9.

Osty deals 12 damage. This card costs 0 -cost if Osty has attacked this turn.

Upgrade: +4 OstyDamage

What Ends Runs with Flatten

Flatten’s most common run-enders are Kaiser Crab Boss (5.8%), The Kin Boss (5.8%), and Knowledge Demon Boss (5.3%).

• Kaiser Crab Boss5.8% of runs
• The Kin Boss5.8% of runs
• Knowledge Demon Boss5.3% of runs
• Decimillipede Elite4.7% of runs
• Test Subject Boss4.7% of runs

See Also

Compare Flatten with the rest of the best Slay the Spire 2 cards, relics, and classes below.