Peri is a pet acquired at a 1 in 7,500 chance for each monster killed in Perilous Peaks.

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Peri
Peri
Pet ID: melvorF:Peri
Source: Perilous Peaks
Drop Chance: 1 in 7,500 (0.01%)
Effect: +5% Melee Evasion
+5% Ranged Evasion
+5% Magic Evasion
Part of 100% Completion: Yes

Having Peri with you as a pet increases the player's evasion ratings by +5%.