Mirrorwyrm (5e Creature)
From D&D Wiki
Large monstrosity, unaligned
Spell Reflection. The mirrorwyrm is immune to all spells cast at 3rd level or below. If it is targeted by spell at or below 3rd level, the caster is instead affected.
Multiattack. The mirrorwyrm makes a bite attack if it is not currently grappling a creature in this way, and then makes two claw attacks.
Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 16 (3d8 + 4) piercing damage. A creature hit by this is immediately grappled.
Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 4) slashing damage.
A miracle of evolution in itself, the Mirrorwyrm is more than just deadly. The Varanus Specupellis is a very large climbing reptile, found sulking in the various caves and late at night near them.
The most striking feature you'll notice, if you even manage to see the lizard itself, is the perfectly reflective material that coats its body, the appearance of small shards of glass running up and down its body. However, further evolutionary strangeness comes from its near magical immunity. Almost every magic user that has seen it, likely only a dozen people, has been completely unable to harm or hinder it with spells, and more often than not become harmed in the process. This is incredibly odd, as Batheron's Heel hasn't seen much magic, let alone had the time to evolve resistance.
Besides the resistance, it is a rather normal ambush predator. It spends most of it's time in caves, more often than not by itself, waiting. Every few nights, they leave, often rolling around in mud first to hopefully prevent the shine of it's scales, where it then scavenges for anything it can eat. It is helped by the mirrorwyrm being unnaturally stealthy, able to sneak up on most prey in its natural habitat.