A Tressym turned into a vampire by the party using the Vampiric Blood Infuser.
Small undead (shapechanger), neutral evil
Armor Class 13 (natural armor) Hit Points 27 (6d6 + 6) Speed 40 ft., fly 60 ft.
STR 6 (-2)
DEX 16 (+3)
CON 12 (+1)
INT 12 (+1)
WIS 14 (+2)
CHA 10 (+0)
Skills Perception +4, Stealth +5 Damage Resistances Necrotic Condition Immunities Poisoned Senses Darkvision 60 ft., Passive Perception 14 Languages understands Common and Abyssal but can't speak
Challenge 1 (200 XP)
Shapechanger. Canto can use its action to polymorph into a Tiny beast or back into its true form. While in beast form, Canto retains its undead status but cannot use its bite attack. Its statistics are otherwise the same. It reverts to its true form if it dies.
Keen Smell. Canto has advantage on Wisdom (Perception) checks that rely on smell.
Incorporeal Movement. Canto can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.
Regeneration. Canto regains 5 hit points at the start of its turn if it has at least 1 hit point and isn't in sunlight. If Canto takes radiant damage or damage from holy water, this trait doesn't function at the start of its next turn.
Actions
Bite. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 6 (1d8 + 2) piercing damage. The target must succeed on a DC 11 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.
Blood Drain (Recharge 5-6). Canto targets one creature it can see within 5 feet of it that has 0 hit points and is unconscious. The target must make a DC 11 Constitution saving throw, taking 14 (4d6) necrotic damage on a failed save or half as much on a successful one. Canto regains hit points equal to the damage dealt.
Shadow Pounce. Canto magically teleports up to 30 feet to an unoccupied space it can see. Before or after teleporting, Canto can make one bite attack.