Yeast, Host of Mask

Bound. Yeast is magically bound to a master. As long as Yeast and its master are on the same plane of existence, the master's wearer can telepathically Yeast to travel to it, and Yeast knows the distance and direction to the master. If Yeast is within 60 feet of the master, half of any damage the master takes (rounded up) is transferred to Yeast.

Regeneration. Yeast regains 10 hit points at the start of its turn if it has at least 1 hit point. 

Sneak Attack. Mask knows how to strike subtly and exploit a foe's distraction. Once per turn, you can deal an extra 2d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.

You don't need advantage on the attack roll if another enemy of the target is within 5 feet of it, that enemy isn't incapacitated, and you don't have disadvantage on the attack roll.

Flowing Strikes. Yeast's attacks count as finesse attacks.  

Multiattack. The guardian makes two spike attacks or two throwing shard attacks.

Spike. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (3d6 + 4); piercing damage. 

Throwing Shard. Ranged Weapon Attack: +7 to hit, reach 60 ft., multiple targets. Hit: 8 (3d4 + 4); piercing damage

Can cast the spell Darkness once per day as an action

Cunning Action. Yeast's quick thinking and agility allow you to move and act quickly. You can take a Bonus Action on each of your turns in Combat. This action can be used only to take the Dash, Disengage, or Hide action.

Shroud. When a creature makes an attack against the master of the Yeast, they grant a +2 bonus to the wearer's AC if Yeast is within 5 feet of the master. 

Uncanny Dodge. When an attacker that Yeast can see hits them with an attack, you can use Yeast's reaction to halve the attack's damage against them.