The Byrdonis Egg is one of the most satisfying early rewards you can stumble across in Slay the Spire 2. It asks a little patience from you, but the payoff is a free, zero-cost attack card that hits harder than a basic Strike at twice the energy efficiency. If you've seen this mysterious unplayable card sitting in your deck and wondered what to do with it, this guide covers every step from finding the egg to hatching it and deciding whether it's worth your campfire stop.
Byrdonis Egg in your deck
Where Do You Find the Byrdonis Egg?
The Byrdonis Egg comes from a specific event called Byrdonis Nest, which appears in mystery rooms during Act 1. These rooms are marked with a question mark (?) on the map, and the event is one of the earlier ones you're likely to encounter in a run.
When you enter the Byrdonis Nest event, you're presented with exactly two choices:
- Eat the Egg and permanently gain 7 Max HP
- Take the Egg and add the Byrdonis Egg quest card to your deck
Neither option carries a hidden penalty. It's a clean, positive fork in the road, which makes the decision purely about what your current run needs most.
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The Byrdonis Nest event is exclusive to Act 1, so this is your only window to pick up the Byrdonis Egg during a run. Don't expect a second chance later.
How to Hatch Byrdonis Egg
Once Byrdonis Egg enters your deck, it's flagged as Unplayable. You cannot use it in combat, and it will show up in your hand like any other card, taking up draw space every time it appears. The sooner you hatch it, the less it disrupts your hand.
To hatch it, head to a Rest Site, which appears on the map as a campfire icon. When you arrive, you'll notice a third option has been added to the usual menu:
- Rest (recover HP)
- Smith (upgrade a card)
- Hatch (hatch the Byrdonis Egg)
Select Hatch, and the quest card is permanently removed from your deck and replaced with Byrd Swoop.
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Choosing Hatch uses your entire Rest Site action. You cannot Rest or Smith at the same campfire, so plan accordingly before committing.
Hatch option at Rest Site
When Should You Hatch It?
The best move is to hatch Byrdonis Egg at the very first campfire you reach after picking it up. Here's why: in the early stages of Act 1, your deck is small, meaning the unplayable egg will cycle into your hand far more frequently than it would later in a run. Every time it appears, it's one less playable card on that turn, which can be punishing against elites or multi-enemy encounters.
Skip the temptation to heal or upgrade at that first campfire. Unless you're critically low on HP and facing an elite immediately after, hatching the egg takes priority.
What Card Does Byrdonis Egg Give You?
After hatching, you receive Byrd Swoop, a Colorless Attack card with the following stats:
For context, a standard Strike deals 6 damage for 1 Energy. Byrd Swoop delivers more than double that output for zero Energy, making it one of the most efficient damage cards available in the early game. Because it's Colorless, every character in the game can use it, so there's no class restriction to worry about.
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Upgrading Byrd Swoop at a future Smith stop is absolutely worth it. Going from 14 to 18 damage for free is a significant bump, especially in longer Act 1 and Act 2 fights.
Byrd Swoop card stats
Is Byrdonis Egg Worth Taking?
In most situations, yes. The Byrd Swoop card you receive is stronger than the 7 Max HP alternative for the majority of builds and playstyles. A free 14-damage attack fits naturally into almost any deck, and the zero-energy cost means it never competes with your other cards for resources.