Initial pass at unicorn pack.

README.md

@@ -83,9 +83,8 @@ Most trophies after round 6 wins.
 
 ## Packs
 
-Two card packs are playable, chosen by the host in the lobby (a third,
-Unicorn, is stubbed for later). Each pack is six tiers, one per round, and
-every pet ships as two copies.
+Three card packs are playable, chosen by the host in the lobby. Each pack is
+six tiers, one per round, and every pet ships as two copies.
 
 ### Turtle pack
 
@@ -120,6 +119,36 @@ The Golden pack adds mechanics the Turtle pack doesn't have:
 - **Cockatoo** — a shop-time reveal, plus Manta Ray's free first buy,
   Blue-Ringed Octopus' per-buy apples, and more.
 
+### Unicorn pack
+
+| Tier | Pets | Food |
+| ---- | ---- | ---- |
+| 1 | Alchemedes, Cuddle Toad, Pengobble, Barghest, Basilisk, Baku | — |
+| 2 | Thunderbird, Gargoyle, Frost Wolf, Mothman, Nightcrawler, Bigfoot | Fairy Dust |
+| 3 | Fur-Bearing Trout, Calygreyhound, Tatzelwurm, Skeleton Dog, Mandrake, Lucky Cat, Slime | Water of Youth |
+| 4 | Roc, Chimera, Kraken, Unicorn, Abomination, Rootlin, Fairy | Health Potion |
+| 5 | Kitsune, Pixiu, Red Dragon, Amalgamation, Vampire Bat, Werewolf, Loveland Frogman | Big Mana Potion |
+| 6 | Sleipnir, Sea Serpent, Bakunawa, Manticore, Team Spirit, Behemoth, Quetzalcoatl | Cornucopia |
+
+The Unicorn pack adds two mechanics the others don't have:
+
+- **Mana** — a **persistent** resource (unlike ephemeral Trumpets): pets earn
+  it in the shop (Cuddle Toad, Thunderbird, Roc) and in battle (Alchemedes,
+  Fur-Bearing Trout, Kitsune, Tatzelwurm per rock blank), and spend it to power
+  abilities (Pengobble, Gargoyle, Sea Serpent, Bakunawa; Sleipnir's very Power
+  equals your Mana). It carries over between rounds until spent, so you can bank
+  it up.
+- **Ailments** — temporary debuff cards attached to a pet during battle,
+  removed at round end like apples. **Spooked** lowers the pet's clash attack
+  (−1 each, min 0); **Exposed** raises the damage it takes per hit (+1 each).
+  They stack, can be added to the enemy pet or dropped on top of the enemy deck
+  (Frost Wolf, Slime, Kraken, Red Dragon). **Baku** shrugs off the first one it
+  takes, **Unicorn** turns the next friendly one into apples, and **Manticore**
+  makes enemy ailments count for more.
+- Plus a **game-wide discard pile** the higher tiers reach into (Chimera,
+  Abomination), pet-recycling (Fairy, Loveland Frogman's bounce), and shop
+  tricks — Bigfoot's deck peek, Water of Youth's upgrade, Quetzalcoatl's reveal.
+
 ## Layout
 
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