Corrupted Beetle

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 12 (2d8) piercing damage.

Slam. Melee Weapon Attack: +4 to hit, reach 10 ft., one target. Hit: 12 (2d8 + 4) bludgeoning damage.

Acid Ray. (Recharge 5–6). The Corrupted Beetle shoots acid ray at one or two creatures it can see within 60 feet of it. It can use ray only once on a turn.
Acid Ray. The target must make a DC 17 Constitution saving throw, taking 47 (6d10) acid damage on a failed save, or half as much damage on a successful one.

Spell Reflection. If the beetle makes a successful saving throw against a spell, or a spell attack misses it, the beetle can choose another creature (including the spellcaster) it can see within 30 feet of it. The spell targets the chosen creature instead of the beetle. If the spell forced a saving throw, the chosen creature makes its own save. If the spell was an attack, the attack roll is rerolled against the chosen creature.
It can be used twice per day.

Opportunity attack. Leaving the beetle's mele range it triggers its slam attack