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 27 recorded runs, decks running it win 11.5% of the time, trailing the 12.6% average by 1.1%. It’s a more selective pick, turning up in just 5.2% of decks that could run it. Necrobinder players keep it in 15.7% of their runs, so it’s a familiar sight in those decks. On average it shows up 1.2 times in the decks that take it.

It performs best next to Hang — together they post a +88.5% swing in win rate. It also has strong chemistry with the relic Gorget, which moves its win rate by +38.5%. At 2 energy, it’s upgraded in 12.5% 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 3 wins, 23 deaths, and 1 abandoned runs with it in the deck. The encounter that most often ends a run carrying it is Skulking Colony Elite, which closes out 11.1% 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 Hang (+88.5%), Haunt (+55.1%), and Undeath (+38.5%).

Hang+88.5%3 runsHaunt+55.1%3 runsUndeath+38.5%4 runsNecro Mastery+28.5%5 runsDeath March+21.8%3 runsFriendship+21.8%3 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 11.5% win rate across 27 runs.

The Necrobinderappears in 15.7% of its runs (27 tracked)

Best Relics for Flatten

Flatten pairs best with the relics Gorget (+38.5%), Potion Belt (+28.5%), and Gremlin Horn (+21.8%), ranked by win-rate lift.

Gorget+38.5%4 runsPotion Belt+28.5%6 runsGremlin Horn+21.8%3 runsBag of Preparation+21.8%4 runsPen Nib+21.8%3 runsAmethyst Aubergine+21.8%3 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 12.5% 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 Skulking Colony Elite (11.1%), Bygone Effigy Elite (7.4%), and Infested Prisms Elite (7.4%).

• Skulking Colony Elite11.1% of runs
• Bygone Effigy Elite7.4% of runs
• Infested Prisms Elite7.4% of runs
• The Kin Boss7.4% of runs
• Hunter Killer Normal7.4% of runs

See Also

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