TL;DR
Stacy is not one boss. She is whichever boss you build for yourself in the event that runs right before the fight. Four choices, each a small menu, and every option you accept makes Stacy stronger while every "No Thanks" damages your own cat instead. There are 256 possible versions of her. Your job is to read the pre-fight event like a shopping list and pick the Stacy your team can actually beat. The single biggest lever is the element choice: Fire is melee-safe, Ice forces ranged, Lightning forces spread.
Who Stacy Is
Stacy belonged to Dr. Beanies. The original cat died decades ago, and Beanies has carried the grudge ever since. The thing you fight in The Lab is a clone of her, pulled out of a machine and twisted into something that hits back. The game stamps every copy with a serial number, so you will see Stacy #752903 or #163569 wandering the same zone as numbered trash mobs. Those clones charm, heal, and buff their allies, but they are not the boss. The boss is the Stacy Mutant, and she is the only one worth planning around.
You meet her in The Lab, Chapter 1, Act 3.
Base Stats Before You Change Anything
Strip away every choice and the Stacy Mutant is a small, soft target. The numbers below are her floor.
| Stat | Value |
|---|---|
| Health | 100 (125 Regular, 150 Hard, 175 Crazy, 200 Impossible) |
| Damage | 5 |
| Movement Range | 4 |
| Luck | 5 |
| Size | 1x1 |
| Type | Cat |
A 100-health, 5-damage cat is nothing. Everything dangerous about this fight comes from what you let her pick up in the event.
The Four Choices Build Your Boss
The pre-fight event hands you four decisions in a row. Each one offers three buffs for Stacy plus a "No Thanks." Accepting a buff makes the fight harder. Declining it spares Stacy but lands a penalty on your cat. So a "No Thanks" is never free. You are trading an easier boss for a worse roster, and sometimes that trade is right.
Choice 1, the defensive layer. Stacy can take Thorns (+3, reflects damage back at melee attackers), Brace (+3, mitigation against incoming hits), or Holy Shield (+7, negates whole instances of damage). Decline and your cat eats a random general disorder plus 3 Poison. Holy Shield is the nastiest of the three for a ranged team because it eats single big hits cleanly. You burn through it with multi-hit moves like item:tinkerer-refine-materials and item:butcher-chomp, or you cleave it off with abilities that hit around the target.
Choice 2, the element. This is the choice that decides the whole fight.
- Fire gives Stacy Spit Lava (2 damage, 1 Burn, drops a Lava Tile) and Flamethrower (3 damage cone, 2 Burn), and makes her Fire-immune. The lowest raw damage of the three. Burn stacks over time, so a melee team survives this as long as it has cleanse or sustain.
- Ice gives her Ice Breath (4 damage cone, 1 knockback) and item:hunter-shards of Ice (6 damage, always Freeze), and makes her Ice-immune. This is the melee trap. Shards Freeze every time and the breath knocks you around, so a melee roster gets locked down at exactly the range it needs. Bring ranged cats.
- Lightning gives her Lightning Dash (6 damage) and Lightning Storm (3 damage AoE, 10% Stun chance), and makes her Electric-immune. The most aggressive build. The loss condition is a Stun snowball on a clumped team, so spread your formation wide enough that one pattern cannot catch two cats.
- Decline the element entirely and your cat takes a random disorder and a random parasite, while Stacy is left swinging a basic punch and a item:mage-magic-missile. A toothless boss for a damaged cat.
Choice 3, the stat shift. Health Up, Speed Down (+25 Health, -2 Speed). Damage Up, Health Down (+2 Damage, -25 Health). Speed Up, Damage Down (+6 Speed, -1 Damage). Decline and your cat takes all 7 basic Injuries, a permanent All Stats Down. That penalty is brutal and follows the cat past this fight, so most runs should accept one of the three stat trades rather than cripple a teammate. Damage Up, Health Down is the one to take if you can kill fast; it drops her to a glassier target.
Choice 4, the special. Double Head (an extra turn each round). Third Paw (counters melee and inflicts Bleed on hit). Mirror Shine (reflects projectiles, emits a Sparkle each turn). Decline and your cat gets a random disorder, No Health Regen, and No Mana Regen. Mirror Shine is the trap for ranged teams because it turns your own projectiles against you. If you see Mirror Shine offered and your damage is projectile-based, that is your signal to lean melee and cleave instead.
How To Actually Pick
Read the element first and pick the one that matches the team you walked in with. If you brought melee bruisers, take Fire and play through the Burn with sustain. If your damage is mostly ranged, take Ice; the immunity costs you nothing and you stay out of Shards range anyway. If you have a mobile, spread-out roster, Lightning is fine as long as nobody clumps.
After the element, the rest is damage control. Avoid stacking a defensive layer you cannot break: skip Holy Shield on a single-hit ranged team, skip Thorns on a melee team. On the stat choice, take a real trade rather than the all-Injuries penalty; the permanent stat loss on your cat outweighs almost any boss buff. On the special, the only one that should change your plan is Mirror Shine against projectiles.
For the ranged-damage answer this fight rewards, the hunter glass cannon build brings the reliable out-of-range pressure you want against Ice, and the mage elemental AoE build covers the multi-hit cleave that strips Holy Shield. If you would rather understand the debuffs Stacy stacks on you, the status effects guide lays out every Burn, Freeze, and Stun interaction in this fight.
Winning The Fight
Scout before you commit. Spend the first turn or two watching which pattern Stacy throws, then move your formation to answer it instead of locking yourself into a stance on turn one. Keep the pressure on her health bar; this is a tempo fight, and dragging it into attrition favors whichever buffs she stacked. Bring reliable ranged damage, one reposition or mobility tool to break out of Freeze and knockback, and enough sustain to absorb repeated pressure.
Her 100 base health is the whole point. Hit hard early, refuse to clump against Lightning, stay out of Shards range against Ice, and carry cleanse against Fire. The Stacy you fight is the one you agreed to. Choose her well.