From Melvor Idle
This page is up to date (v1.2.2).
Pet ID: melvorD:Mac
Source: Volcanic Cave
Drop Chance: 1 in 200 (0.50%)
Effect: +1% Damage To Slayer Area Monsters
Part of 100% Completion: Yes

Mac is a boss pet acquired by completing the Volcanic Cave.

The name is a shorter version of Malcs, the boss of Volcanic Cave (and name of The Developer), implying Mac is Malcs' baby dragon.