Crag Fiend

Nondetection. The Fiend cannot be targeted or detected by any divination magic or perceived through magical scrying sensors.

Pounce. If the Fiend moves at least 20 feet straight toward a creature then hits it with a claw attack on the same turn, that target must succeed on a DC16 Strength saving throw or be knocked prone. If the target is prone, the Fiend can make one bite attack against it as a bonus action.

Improved Spell Turning. The Fiend has advantage on saving throws against spells and spell attack rolls have disadvantage against it. If the Fiend's saving throw succeeds against a spell that targets only it and the spell is of 7th level or lower, the spell has no effect and instead targets the caster.

Multiattack. The Fiend makes two Claw attacks. It can replace one of the attacks with a Bite attack.

Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) slashing damage plus 7 (2d6) necrotic damage.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 22 (4d8 + 4) piercing damage, and the target's Strength score is reduced by 2 (1d4). The target is killed if this reduces its Strength to 0. The reduction lasts until the target finishes a short or long rest.

Spell Riposte. If a spell attack misses the Fiend, it can use its reaction to reflect the spell, targeting the caster. The Fiend makes a spell attack using the spellcasting modifier used in the original attack.