How to Beat Aeonglass, the New Act 3 Boss in Slay the Spire 2

A New Face at the End of Act 3

If you booted up Slay the Spire 2 after June 19 and walked into Act 3 expecting Doormaker, surprise. He’s gone. The v0.107.1 Major Update 2 pulled Doormaker out of the game completely and dropped in a brand new Act 3 boss called Aeonglass.

Mega Crit was blunt about why. Doormaker had interesting moment-to-moment decisions, but it sat over the complexity threshold they wanted for a boss, and it carried lingering balance issues. Rather than keep patching it, they scrapped it and built something new. So if you’ve been reading old Doormaker guides, set them aside. None of that applies anymore.

Aeonglass is a different kind of problem. Doormaker attacked your deck’s rules. Aeonglass attacks your clock.

How Aeonglass Works

The core mechanic is the Wither status card. Here’s the exact text: Wither is a 1-cost Status card with Retain, and at the end of your turn, if it’s still sitting in your hand, you take 2 damage.

That sounds mild. It isn’t, because of two things.

First, Retain means Wither doesn’t leave your hand on its own. A normal Burn or Dazed card clogs your draw and then cycles out. Wither stays. It parks in your hand turn after turn and keeps biting you for damage unless you actively get rid of it.

Second, this scales. Aeonglass keeps handing you more Withers as the fight goes on, and the per-card damage climbs the longer you’re in there. Players on the subreddit describe the scaling as nonlinear. The longer you fight, the more statuses get shuffled in, and the harder each one hits. A fight that looks fine on turn 5 can become unsurvivable by turn 14.

On top of the Withers, Aeonglass throws stat-down turns at you. Expect Strength and Dexterity debuffs that cut your damage and your Block right when you want to be pushing. At higher ascension the health pool is large, around 535 in high-ascension reports, and the Withered spawn passive comes partly pre-stacked, so you get less runway before things spiral.

The One Rule: This Is a Race

Every decent Aeonglass strategy comes back to the same point. You cannot grind this boss down slowly. If you try to trade blows over 20 turns, the Withers win. You bleed out from your own hand.

The number people keep landing on is turn 10 or 11. If your deck can put Aeonglass on the floor by then, you’re in good shape. If it can’t, you need a plan for the Withers, because they will outpace you.

So when you’re building your Act 3 deck, ask one question before you reach this fight: can I deal real, scaling damage fast? If the answer is no, you’re going to have a bad time.

What to Bring

Fast, scaling offense. Card-spam decks actually do fine here, as long as the spam is offensive and scaling. The trap is a wide, durable, do-everything deck that never closes. You want a deck that ramps and kills.

Card removal from hand. Discard and exhaust effects are gold against Aeonglass. Anything that lets you dump cards from your hand at end of turn clears Withers before they tick. If your kit can exhaust or discard a couple of statuses per turn, you take the sting out of the snowball.

Don’t overextend on stat-down turns. When Aeonglass applies the Strength and Dexterity debuffs, your numbers drop. Don’t dump your whole hand into a turn where your damage and Block are gutted. Read the intent, hold back, and spend your big plays on clean turns.

Keep your deck thin. A tight deck with high-impact cards reaches its payoff faster, which matters when you’re trying to close inside 10 turns. Thin decks also draw their answers more consistently.

Per-Character Notes

Silent. Shivs work, but lean on accuracy and Phantom Blades so each Shiv actually counts. You’re trying to burst the boss down inside roughly 10 turns, not nibble. Discard support helps you clear Withers, which plays right into Silent’s strengths.

Regent. Aeonglass came in the same patch that buffed Regent, so this is a good moment to bring it. A Forge build that gets Sovereign Blade scaling early can hit the turn-10 kill window. See our Regent build guide for the post-buff meta.

Ironclad. You want Strength scaling and exhaust support. Exhaust is doubly useful here because it doubles as Wither removal. Get your Power cards down early so your damage keeps climbing while you toss statuses.

Defect and Necrobinder. Both can race if they snowball Orbs or summons. The key is the same: prioritize damage scaling over a slow defensive shell.

A Note on Bugs

Some players have reported that Withers were intended to discard like Burns under certain effects, and there’s been back and forth about whether the current behavior is fully working as designed. This is Early Access, and Aeonglass has been getting tuning passes. If something feels off, check the current patch notes before assuming it’s your fault.

Closing Thought

After a few rounds of tuning, Aeonglass is a well-liked fight, but it asks one question: did you build a deck that kills, or a deck that survives? Survival decks lose here. Bring offense, bring hand cleanup, and end it fast.

If you want the wider picture, our Act 3 boss guide covers the other Glory bosses you might draw instead, and the final boss guide walks you through what comes after. For tracking how all these changes shake out, keep an eye on our patch meta guide.