How to Beat Ascension 20 in Slay the Spire 2 Complete Guide

Last updated: June 2, 2026 | Reading time: 15 min | by STS2 Guide Team

What Changes at Ascension 20

Ascension 20 is where STS2 gets real. All Ascension modifiers are active: enemy HP scaling, elite spawns buffed, bosses have extra abilities, no rest sites, shops more expensive.

Act 1 Strategy The Foundation

Pathing Priority (Act 1)

1. Elite Elite Shop Rest Boss The optimal path. Two elites = 2 relic chances + better card rewards.
2. Avoid: Too many normal enemies (bloat deck), no elites (underpowered for Act 2).

Deck Building (Act 1)

• Target: 25-30 cards by end of Act 1. Not 35+. Not 20-. Just right.
• Skill/Attack ratio: 60% Skills, 30% Attacks, 10% Powers.
• Must-have by Act 1 boss: At least 1 AOE card and at least 1 block scaling.

Act 2 Strategy The Gauntlet

Act 2 is the hardest Act in A20. Enemies hit hard and have annoying mechanics.

Pathing Priority (Act 2)

1. Elite Shop Elite Campfire(Upgrade) Boss
2. Campfire priority: Upgrade your win-condition card. Not "a card you like."

Key Rule: Dont get greedy. Taking 4 elites in Act 2 is suicide. Take 2 elites max.

Act 3 Strategy The End Game

Act 3 enemies have 200+ HP and deal 30+ damage per hit. Your deck needs to be online by now.

Pathing (Act 3)

1. Find the merchant: Buy health potions. At A20, you need every HP advantage.
2. Campfire = Upgrade: Upgrade your scaling cards (Demon Form, Accuracy, Glacier, Scrawl).

Boss Strategy All 3 Bosses

The Guardian (Act 1 Boss)

Phase 1: 80 HP, deals 12 damage + 2 Thorns. Strategy: Kill in 2 turns. Dont let it reach 0 HP slowly it transitions and heals.

Phase 2: 160 HP (total), deals 8x3 hits + 1 big hit. Block the multi-hit (24 damage total).

Hexaghost (Act 2 Boss)

Mechanic: 250 HP. Every 3rd turn: Inferno (deals 2 x number of burns in discard pile). Strategy: Remove Burn cards from your deck. Block 50+ on turn 3, 6, 9.

The Awakened One (Act 3 Boss)

Phase 1: 300 HP. Gains 15 Strength when damaged. The Slow Kill: Deal damage in small chunks. Use block scaling. Kill in 5-8 turns, not 2-3.

This is the #1 A20 Boss Killer. Players who rush the kill die.

Deck Size Rules The Most Important Concept

Your deck gets bigger every floor. You only draw 5 cards per turn. Adding bad cards makes your deck WORSE.

Common A20 Mistakes

1. Taking too many card rewards: Every card is a dilution of your good cards.
2. Not pathing for elites: Elites give relics. Relics win runs. 2 elites per Act minimum.
3. Upgrading the wrong cards: Upgrade your win condition. Not a Strike.
4. Fighting the Act 3 boss at <40% HP: You will die.
5. Not reading enemy intent: The game tells you what enemies will do. Use that info.