Luck explained — what the stat actually changes and when to buy it

Luck is the stat players either ignore or over-buy. It does four separate things, and the value of each one falls off at a different wave.

What Luck changes

Item drops. Enemies have a chance to drop an item crate; Luck raises it. More crates is more free items over a run.
Consumable drops. Fruit drops more often, which is healing and, on characters like Glutton and Chef, damage.
Shop rarity. Higher Luck shifts the shop toward Tier II, III and IV offers. This is the big one in the mid game.
Level-up upgrade rarity. The four upgrade options on each level roll higher tiers with more Luck.

When each part pays

Drops pay for the rest of the run from the moment you buy them, so early Luck is the best Luck. Shop rarity matters most between waves 8 and 15, when a Tier III weapon offer changes the run. Upgrade rarity matters all run but is small.

After wave 15 only the drops still pay, and the money is better spent on damage or Armor. Our rule: stop buying Luck at wave 12 unless the character scales with it.

Characters that scale with Luck

Lucky — +100 Luck and a luck-scaled hit on every pickup; the stat is damage.
King — +50 Luck exists to find Tier IV items, which give him stats.
Druid and Glutton — more consumables means more of their passive.
Curious — item variety is XP, and drops are variety.

Characters that should skip it

Gladiator starts at -30 Luck and does not scale with it, so buying it back is a waste. Hunter cannot harvest and needs every material for Range and Crit. Single-stat builds like Mage get more from Elemental Damage than from a slightly better shop.

Luck and Harvesting

They are often confused. Harvesting is materials paid at wave end and compounds; Luck is odds. Harvesting is the earlier buy on an economy character; Luck is the earlier buy on a fighter who needs the shop to cooperate. See Harvesting explained for the other half.