Musteval

(from Book of Exalted Deeds - 2003):

This slim humanoid creature has the elongated snout, tufted ears, and furtive eyes of a ferret. It has slender limbs, white fur covering its body, and pink eyes. 

Although the least powerful of the guardinals, mustevals nevertheless are unstinting foes against evil. They serve greater celestials as spies, and they often aid humanoid heroes by delivering information about powerful evil creatures. 

They are the only guardinal variety not represented among the Five Companions of Talisid, the Celestial Lion, and harbor some resentment over that fact, which they regard as a simple oversight bound to be corrected very soon. Mustevals are agile and seldom remain still for long. Clever use of their change selfability usually keeps their animalistic features concealed when dealing with other creatures. 

Mustevals stand 2 feet tall and weigh 30 pounds. They speak Celestial. 

Combat: In combat, mustevals remain in constant motion, combining their focused movement and magic missile abilities to good effect. A musteval’s natural weapons, as well as any weapons it wields, are treated as having the good alignment for the purpose of overcoming damage reduction. 

Spell-Like Abilities: At will—detect evil, detect magic, disguise self, magic missile, protection from evil (self only) and see invisibility; 1/day— invisibility (DC 13). Caster level 3rd. The save DCs are Charisma-based. 

Focused Movement: When moving, a musteval can take a move action and a standard action at any point during the move. The musteval cannot take a second move action during a round when it uses its focused movement ability. Mustevals almost always use this ability to move before and after using a spell-like ability during combat. 

Skills: Mustevals have good claws for climbing and sharp hearing. They receive a +4 racial bonus on Climb and Listen checks

(from Planescape: Morte's Planar Parade - 2023):

Mustevals are small, mousy guardinals skilled at evading danger. Their speed, stealthy nature, and illusion magic make them adept spies, scurrying through the multiverse to serve greater forces of good.

MUSTEVAL GUARDINAL (5e)

Small Celestial, Typically Neutral Good

AC 13. HP 38 (11d6), Speed 35 ft.

STR 12 (+1),   DEX 16 (+3),   CON 11 (+0),   INT 14 (+2),   WIS 15 (+2),   CHA 14 (+2)

Saving Throws: Dex +5, Cha +4

Skills: Perception +6, Stealth +7

Damage Resistances: radiant

Condition Immunities: frightened

Senses: passive Perception 16

Languages: Celestial, Common

Challenge 2 (450 XP) Proficiency Bonus +2

Actions:

Multiattack. The musteval makes two Bone Blade attacks.

Bone Blade. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) slashing damage plus 3 (1d6) radiant damage.

Spellcasting. The musteval casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability:

At will: dancing lights

1/day each: disguise self, invisibility

Reactions:

Skirmish Movement. When a creature ends its turn within 5 feet of the musteval, the musteval can move up to half its speed. This movement doesn’t provoke opportunity attacks.