Slay the Spire 2 Aeonglass Boss Guide — Act 3's New Final Boss

Aeonglass is Slay the Spire 2's new Act 3 boss — the replacement for the retired Doormaker. The fight is a slow strangle: a big health pool, a boss that blocks every other turn, and a pressure system that keeps stuffing damage spells into your deck whether you like it or not. Here is the verified pattern and the game plan.

The vitals

• HP: 512 (535 on Ascension 9) — one of the largest pools in the game
• Opening powers: Withering Presence plus 3 stacks of Artifact
• Arena: the Act 3 (Glory) boss slot, no summons or add waves

Withering Presence: the defining pressure

The boss's signature power: every 6 cards you play, a Wither is added to your hand. Wither is a Status that deals 3 (6) damage to you at the end of any turn it spends in your hand.

Read that correctly: the tax is on playing cards. Every engine turn deepens the Wither queue. The three standard answers:

1. Play fast, spend fast. Wither only hurts while it sits in hand at end of turn — turns that empty the hand pay nothing.
2. Exhaust or remove it. Cards like Purity can exhaust multiple Withers at once; any Exhaust-a-card effect converts the tax into fuel.
3. Discard as a stopgap. Discard effects dodge the end-of-turn damage for a turn, but the Wither shuffles back later — a delay, not a cure.

Note the boss's 3 Artifact at the start: your first debuff applications bounce off. Don't waste your one good Vulnerable application into the Artifact wall; strip or wait it out.

The verified moves

• Ebb — deals 22 damage (26 on high Ascension) and gains 33 Block. The turn you see Ebb coming, hold your big attack: 33 Block eats unprepared damage for breakfast. Chip it with multi-hits or save for after.
• Eye Lasers — 11 damage twice (12 twice on high Ascension). The gentler turn; block it comfortably and scale.

The boss cycles between these patterns while Withering Presence grinds on, so the fight is really a resource equation: your hand management versus a 512-point clock.

The game plan

1. Turn 1–3: scale, don't race. Artifact punishes early debuffs, Ebb's Block punishes early burst. Build your engine.
2. Count your cards. Track plays in chunks of six — know when the next Wither arrives and make sure your hand can absorb it.
3. Hold burst for non-Ebb turns, or bring multi-hit attacks that chew 33 Block in slices.
4. Keep one hand-clearing option — an exhaust effect or a big draw turn — for the late fight when Wither pressure peaks.

Keep reading:

• 0.105 Patch Overview
• Class Difficulty Ranking
• The Four Core Mechanics, Explained