Still working thru the Creature Catalog from Dragon Magazine #89. The hyena and giant hyena referenced below have stats that can be found in the DM's Basic Rules.
Large humanoid (gnoll, shapeshifter), chaotic evil
Armor Class 14
Hit Points 58 (9d8 + 18)
Speed 30 ft. (40 ft. in hyena form)
STR DEX CON INT WIS CHA
15 (+2) 13 (+1) 14 (+2) 10 (+0) 11 (+0) 10 (+0)
Skills Perception +4, Stealth +3
Damage Immunities bludgeoning, piercing, and slashing damage from nonmagical weapons that aren’t cold iron
Senses passive Perception 14
Languages Gnoll (can’t speak in hyena form)
Challenge 3 (700 XP)
Shapechanger. The ghuuna can use its action to polymorph into a giant hyena, or back into its true form, which is a large gnoll. Its statistics, other than its AC, are the same in each form. Any equipment it is wearing or carrying isn’t transformed. It reverts to its true form if it dies.
Keen Hearing and Smell. The ghuuna has advantage on Wisdom (Perception) checks that rely on hearing or smell.
Rampage. When the gnoll reduces a creature to 0 hit points with a melee attack on its turn, the gnoll can take a bonus action to move up to half its speed and make a bite attack.
Hyena Empathy. Ghuuna can communicate and empathize with hyenas and giant hyenas. This gives them a +4 racial bonus to checks when influencing the animal’s attitude and allows the communication of simple concepts and (if the animal is friendly) commands, such as "friend," "foe," "flee," and "attack." Any ghuuna encountered is 80% likely to be accompanied by 2 hyenas (70%) or 1 giant hyena (30%) being kept as pets or guards.
Bite (hyena form only). Melee Weapon Attack: +4 to hit, reach 5 ft., one target.
Hit: 10 (2d6 + 3) piercing damage. If the target is a gnoll, it must succeed on a DC 12 Constitution saving throw or be cursed with ghuunism.
Bite. (Gnoll Form Only) Melee Weapon Attack: +4 to hit, reach 5 ft., one creature.
Hit: 4 (1d4 + 2) piercing damage.
Greatsword (Gnoll Form Only). Melee Weapon Attack: +4 to hit, reach 5 ft., one creature.
Hit: 7 (1d10 + 2) slashing damage.
Ghuuna (the form is singular and plural) are the result of a special quasi-lycanthropy created by Yeenoghu that affects only gnolls, causing them to shapechange into a hyaenodon form. Ghuuna are affected by stress and phases of the moon like other lycanthropes.
In their normal (unchanged) form, ghuuna appear to be large gnolls. In this form they shun armor and usually carry greatswords as weapons. In both forms, ghuuna have 60 ft. darkvision and acute senses of hearing and smell.
Ghuuna can speak the usual languages a gnoll may know. They rarely intentionally spread "ghuunism" among gnolls, preferring to be "the few and the proud."