Build a loot table

A loot table decides what an item roll returns. It is a set of weighted entries: higher weight means an entry is drawn more often. One entry can be nothing, so not every roll pays out.

Loot table: storm-cache
entry: storm-glass    weight: 2
entry: copper-ring    weight: 18
entry: (nothing)      weight: 30
pity tier: Rare

Weights are relative

Only the ratios matter. In the table above a roll returns nothing about six times in ten, a Copper Ring most of the rest, and the Storm Glass rarely. To make the Storm Glass more common, raise its weight or lower the others.

Add pity so streaks stay fair

The pity tier raises the odds of a Rare or better drop after a dry streak, then resets when it pays out. It is per viewer and per table, so one viewer's luck never spends another's. Pick a tier that is a genuine reward but not your rarest.

You do not set the exact rarity odds here directly; those come from the per-rarity multipliers, which the next step covers.