Based on the dire wolf an a twig blight, this creature is a essentially a large wolf-like construct made of wood, held together by arcane magic.
Large Construct, unaligned
Armor Class 14 (natural armor)
Hit Points 37 (5d10 + 10)
Speed 50 ft.
Damage Resistance psychic; bludgeoning and piercing from nonmagical weapons that aren't adamantine
Damage Immunities poison
Condition Immunities blinded, deafened, exhaustion, poisoned,
Damage Vulnerabilities fire, slashing
Skills Perception +3, Stealth +4
Senses passive Perception 13
Challenge 3 (450 XP)
Fragile Frame. When the wolf dies, it falls apart into non-magical wood. Indistinguishable from broken branches.
Keen Hearing and Smell. The wolf has advantage on Wisdom (Perception) checks that rely on hearing or smell.
Pack Tactics. The wolf has advantage on an attack roll against a creature if at least one of the wolf’s allies is within 5 feet of the creature and the ally isn’t incapacitated.
Pounce. If the wolf moves at least 20 feet straight toward a creature and then hits it with a claw attack on the same turn, that target must succeed on a DC 13 Strength saving throw or be knocked prone. If the target is prone, the tiger can make one bite attack against it as a bonus action.
Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) piercing damage. If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone.
Claw. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 4) slashing damage.
Would this creature be a level 3 challenge rating? Are there things that I missed in the description the make the creature too OP or UP? Is Slashing damage a good vulnerability? What level should my players be before I introduce this creature in a pack of 3-5? for that matter, how many of these creature would be a good number to introduce the creatures in a first encounter?