Demon Altar

Summons one demon per level. For each dead ally, grows permanently stronger (+0.1 raw per death since Patch #30).

How players use it

King of Greed Support: a Dispenser early, since it gains attack speed for every gold earned (Vao, Aevean). Vaults with Speculation are an income alternative, and a Blood Demon Altar grows from every Mercenary that dies.
King-difficulty achievements Self-Sufficient (17.7%): win on King with no perks. Vao credits the player Clyde with a Nomads route: re-roll for the King of Nature first to get Procreate’s 9 units, avoid Progress, Time and Stone, and put three Mobs beside a Cemetery and Demon Altar taken from Blood.

In the King of Blood's 9-card deck: a run as this king can start with it, and losing a battle offers cards from your own deck.
Loot after beating the King of Blood in battle when that king is one of your enemies.
Merchant: Jack of Structures (buildings, towers and bases).
Joker mode: pick it for a custom deck.

Entry	Effect
Covenant King of Blood decree	Doubles the stats of all active Demon Altars.
Pagan King of Blood perk	Start with a Demon Altar in a random corner plot.

Patch #18 2025-11-11
Demon's Altar now gets buffs when you destroy troop plots with destruction cards.
Patch #18 2025-11-11
Forest now works with Demon's Altar and Cemetery.
Patch #18 2025-11-11
Swords buff numbers were corrected when used on Demon's Altar.
Patch #19 2025-11-21
Forest now properly works with Demon's Altar and Cemetery.
Patch #19 2025-11-21
Shields now works with Demon's Altar and Cemetery.
Patch #23 2026-05-08
Demon's Altar no longer gets an unintended extra boost when Echoformed.
Patch #29 2026-07-29
Demon Altar: Demon's Altar is just now just called Demon Altar.
Patch #30 2026-09-15
Demon Altar damage gained upon units deaths was doubled. All level up buffs when an Altar is leveled up were also increased. NOTE: Demon Altar buff calculation is now transparent: instead of showing +0.5% of the Demon's original base damage, it now shows a +0.1 raw buff. While the initial number you see might feel lower, this is actually a big buff to Demons.
1.0 2026-11-12
Demon Altar now displays troop count and a "recruit" pop-up when it levels up (specific feature of a Tower card)

Lines from the official Steam patch notes since Patch #18 that name this card.

Data: 9 Kings 1.0 card table on the official wiki, imported 2026-11-13.