Chainbreaker: rare, very strong original creature (twin-axe cleave, restless without fights)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

DESIGN.md

@@ -78,6 +78,11 @@ An original dungeon management game (genre: dungeon building & defence) that run
 - **Torture chamber**: one prisoner per 2 tiles. Defeated heroes are knocked out (if there is room) and carried in by imps; torture drains their HP over ~100 s, ~40% defect (paladins ~25%) and become own creatures (needs, wage, lair). Attracts the **Jailer** (6+ tiles): tanky melee that pulls enemies in with a chain
 - **Temple**: creatures pray for mana (more than studying) and mood. Attracts the **Flame Priestess** (6+ tiles): fireballs with splash damage, heals creatures, heals the Soul Core (~8 HP/s) when it is below 90% and no fight is nearby
 
+## Chainbreaker (rare creature)
+- Original design: massive obsidian demon with glowing cracks, broken chains and twin axes; very strong (600 HP, 36 attack), its axes also hit a second enemy nearby
+- Comes through the portal only rarely, and only to great dungeons: 40+ room tiles, a creature of level 5+, 4000+ gold; only one at a time
+- Restless: after two minutes without a fight its mood sinks
+
 ## Hero wave AI
 - Each wave picks an **entry point** on the border of the realm facing the hero gate: few towers/creatures, no reinforced walls and a short way are attractive, entry points of recent waves are avoided, plus some randomness
 - Waves of **6+ heroes split into two groups** with different entry points (the paladin goes with the bigger group)