Should I upgrade Flatten in Slay the Spire 2?

Compare the upgraded text: Osty deals 16 damage. This card costs 0 Energy if Osty has attacked this turn.. If the upgrade lowers cost, adds damage/block, or enables a combo piece, it is usually high priority.

What builds use Flatten?

Flatten appears in 1 tracked build: Osty's Warband (A-tier, core card).

What character uses Flatten?

Flatten is tagged as a Necrobinder card. See the Necrobinder build hub for archetypes that care about it.

Updated for Data 2026-03-17Early Access — numbers may shift with patches.

Flatten

Necrobinder · Attack · Common · 2 cost

Base

Upgraded

Card text

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

Flatten+

Osty deals 16 damage. This card costs 0 Energy if Osty has attacked this turn.

Builds that use Flatten

Archetypes that draft this card in real runs, with the role it plays.

AOsty's WarbandNecrobinder · Core card

Build context

See the Necrobinder build hub for archetypes that feature this card in real runs.

Related cards

Flatten FAQ

Should I upgrade Flatten in Slay the Spire 2?: Compare the upgraded text: Osty deals 16 damage. This card costs 0 Energy if Osty has attacked this turn.. If the upgrade lowers cost, adds damage/block, or enables a combo piece, it is usually high priority.
What builds use Flatten?: Flatten appears in 1 tracked build: Osty's Warband (A-tier, core card).
What character uses Flatten?: Flatten is tagged as a Necrobinder card. See the Necrobinder build hub for archetypes that care about it.

Patch history

SpireForge snapshots card text from Untapped exports dated 2026-03-17. When Mega Crit ships a balance patch, we re-run the scraper and refresh every affected URL—see /patches for the editorial log.