Crystal Reaper Elemental

Earth Glide: The Crystal Reaper Elemental can burrow through nonmagical, unworked earth and stone. While doing so, the Crystal Reaper Elemental doesn't disturb the material it moves through.

Reverbertating Crystal: Whenever the Crystal Reaper Elemental is affected by a sound based effect the effect is recast centered on it with in all directions with its range halved and only once per attack or effect.

The Crystal Reaper Elemental is not immune to these effects however.

Crystal Shredder: The Crystal Reaper Elemental deals one additional damage die on a critical hit.

Reckless: The Crystal Reaper Elemental has advantage on its weapon attacks, however any creature attacking it has advantage on its attacks against it.

Magic Resistance: The Crystal Reaper Elemental has advantage on saving throws to avoid spells and spell like effects.

Magic Reflection: Whenever the Crystal Reaper Elemental is affected by a spell of 6th level or lower the caster must roll a d6, on a 4 or 5 the spell fails to affect the Crystal Reaper Elemental on a 6 the spell is reflected towards the caster, being recast targeting it or with it as the center of the spell area if possible.

Radiance Surge: Whenever the Crystal Reaper Elemental would take radiant damage it instead reflects that damage (this effect hapens before damage calculation ignoring effects that would ignore resistance or immunity to radiant damage), all creatures within 15ft of the Crystal Elemental must succeed in a DC 20 Constitution saving throw taking radiant damage equal to half of the damage that would have been dealt to the Crystal Reaper Elemental instead.

Immutable Form: The Crystal Reaper Elemental is immune to effects that would alter its form such as the polymorph spell.

Crystaline Sharpness: Slashing damage dealt by the Crystal Reaper Elemental ignores resistance to slashing damage, and deals half as much damage to immune creatures.

Deep Wounds: Creatures dealt slashing damage by the Crystal Reaper Elemental must succeed in a DC 20 Constitution saving throw, beeing deeply wounded on a failure, a creature wounded this way takes 1d10 necrotic damage at the end of their turn, until it dies or otherwise spends its action tending to the wound or by healing at least 5 hit points.

Multiattack: The Crystal Reaper makes three attacks on its attack action or two attacks and uses one of its available action.

Crystaline Slash: Melee Weapon Attack +12, 15ft reach, one target, for 3d12+7 slashing damage.

This attack scores a critical hit at a 19 or 20.

Whenever this attack scores a critical hit and the target is reduced to 0 hit points it suffers a fatal slash potencialy decepating or choping of a big part of the body potencialy dying instantly, unless able to survive under those conditions.

Reaper Crystal Blade: All creatures within 15ft of the Crystal Reaper Elemental must succeed in a DC 20 Dexterity saving throw taking 3d12+7 slashing on a failure.

Agressive: The Crystal Reaper Elemental can use the dash action as a bonus action.