Mark is a pet acquired differently from other skill pets, and is unlocked when the player reaches the mark level of 4 in each of the base game Summoning marks.

This page is up to date (v1.3.1).
Mark
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Pet ID: melvorF:Mark
Source:
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Summoning
Drop Chance: See: Acquiring Pets
Effect: +10% Chance to preserve Summoning Charges
Part of 100% Completion: Yes