Brimstone Staff is the 106th most-used weapon under the current filters (0.2% of 497,692 recorded fights), winning 63.0% overall - 6.6% of its wins come against better-geared opponents.
Best against Hallowfall (100.0%), Wailing Bow (71.4%), Realmbreaker (69.2%). Struggles against Energy Shaper (30.0%), Longbow (45.9%), Bloodletter (46.5%).
Winrate by IP difference (50-IP buckets, dot size = sample size). A flat curve means the weapon carries regardless of gear; a steep one means it only wins when out-gearing.
