Should I upgrade Furnace in Slay the Spire 2?

Compare the upgraded text: At the start of your turn, Forge 6.. If the upgrade lowers cost, adds damage/block, or enables a combo piece, it is usually high priority.

What builds use Furnace?

Furnace appears in 1 tracked build: The King's Smith (S-tier, core card).

What character uses Furnace?

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

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

Furnace

Regent · Power · Uncommon · 1 cost

Base

Upgraded

Card text

At the start of your turn, Forge 4.

Furnace+

At the start of your turn, Forge 6.

Builds that use Furnace

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

SThe King's SmithRegent · Core card

Keywords

Forge

Build context

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

Related cards

Furnace FAQ

Should I upgrade Furnace in Slay the Spire 2?: Compare the upgraded text: At the start of your turn, Forge 6.. If the upgrade lowers cost, adds damage/block, or enables a combo piece, it is usually high priority.
What builds use Furnace?: Furnace appears in 1 tracked build: The King's Smith (S-tier, core card).
What character uses Furnace?: Furnace is tagged as a Regent card. See the Regent 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.