Spun Spider Silk

Your loot bias is the “+X% Rare Loot Chance” on the game's Stats screen. Each drop is picked from a weighted table, and your bias changes every weight in it by the game's own formula:

Here bias is 100 + X, minWeight is the table's rarest drop and maxWeight its most common. The rarest drop gains X% of itself, so 100 doubles it. The most common gains nothing, and the ones in between gain a little. At 100 on the Alpha Boar, Dice of Karma I goes from 1/861 to 1/434 and the Alpha Tusk Greatbow from 1/172 to 1/144.

A list that holds more than one table, like a crop field's crop and pet food, shows no chance of yours: we don't have data yet on where one table ends. Rifts show none either: we don't have data yet on how loot bias works there.