Sources
CR
Type
Size
Alignment
Movement

Tressym

Tiny Monstrosity, Any alignment

Armor Class 12
Hit Points 5 (2d4)
Speed 40 ft., fly 40 ft., climb 30 ft.
STR
3
-4
DEX
15
+2
CON
10
+0
INT
11
+0
WIS
12
+1
CHA
12
+1
Skills Perception +5, Stealth +4
Damage Immunities poison
Condition Immunities Poisoned
Senses darkvision 60 ft., passive Perception 15
Languages understands Common but can't speak
Challenge 0 (10 XP)

Traits

Detect Invisibility. Within 60 feet of the tressym, magical invisibility fails to conceal anything from the tressym's sight.

Keen Smell. The tressym has advantage on Wisdom (Perception) checks that rely on smell.

Poison Sense. The tressym can detect whether a substance is poisonous by taste, touch, or smell.

Familiar. With the DM's permission, a person who casts the find familiar spell can choose to conjure a tressym instead of a normal cat.

Actions

Claws. Melee Weapon Attack: +0 to hit, reach 5 ft., one target. Hit:1 slashing damage.