Smaragdine Golem

The golem is immune to any spell or effect that would alter its form.

The golem has advantage on saving throws against spells and other magical effects.

The golem's weapon attacks are magical.

As a bonus action, the golem targets any creature, object, or magical effect within 10 feet of it. The golem chooses a spell already cast on the target. If the spell is of 3rd level or lower, the golem absorbs the spell and it ends. If the spell is of 4th level or higher, the golem must make a check with a +9 modifier. The DC equals 10 + the spell's level. On a successful check, the golem absorbs the spell and it ends. The golem's body glows when it absorbs a spell, as if under the effect of a light spell. A smaragdine golem can only hold one absorbed spell at a time.

The golem makes two slam attacks.

Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 25 (4d8 + 7) bludgeoning damage.

The golem can release an absorbed spell effect as a blast of green energy, which blasts out as a sphere centered on the golem with a radius of 10 feet per level of the absorbed spell. All creatures in the area of effect other than the golem takes 7 (2d6) lightning damage per level of the absorbed spell, or half damage with a successful DC 18 Dexterity saving throw. Creatures that fail the saving throw are also blinded until the end of the golem's next turn.