Darkvision 60 ft., passive Perception 10
Keen Smell. The rat has advantage on Wisdom (Perception) checks that rely on smell.
Enrage. When 6 of the Vermin Lord's allied rats or 2 of the Vermine Lord's allied Rat Swarms are slain within it's line of sight, or it is reduced to half HP (33 or lower), the Vermine Lord Rat becomes enraged, gaining access to Enraged Actions, and the following traits:
Evasion. If the Vermin Lord is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, the Vermin Lord instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.
Feral Speed. While Enraged, the Vermin Lord gains 10 bonus Movement speed.
Improved Resistances. While Enraged, the Vermin Lord gains resistance to acid and Necrotic Damage.
Multiattack. The Vermine Lord makes two Bite attacks
Bite. Melee Attack Roll: +3, reach 5 ft. Hit: 10 (3d4+3) Piercing Damage plus 6 (3d4) Poison Damage.
Vermin's Call (Recharge 5-6). The Vermin Lord Rat calls to it's swarm, summoning 1d6+2 rats or 1 swarm of rats within 15 ft. of itself
Improved Vermin's Call. While Enraged, each time the Vermin Lord Uses it's Vermin's Call action, it may make one Bite attack at a target in range and 2 Plague Bearer Rats are summoned within 15 ft. of the Vermin Lord.