Corrupted Treant

False Appearance. While the Treant remains motionless, it is indistinguishable from a normal tree.

Siege Monster. The Treant deals double damage to objects and structures. 

Ice blast. Ranged Weapon Attack: +10 to hit, range 60/120 ft., 1 target. Hit: 19 (4d6 + 5) cold damage. 

Lightning blast. Ranged Weapon Attack: +10 to hit, range 60/120 ft., 1 target. Hit: 19 (4d6 + 5) lightning damage.

Fire blast. Ranged Weapon Attack: +10 to hit, range 60/120 ft., 1 target. Hit: 19 (4d6 +5) fire damage

lightning bolt (recharge 6). The Corrupted Treant shoots lightning in a 60-foot line that is 5 feet wide. Each creature in that line must make a DC 18 dexterity saving throw, taking 28 (8d6) lightning damage on a failed save, or half as much damage on a successful one.

Ice burst (recharge 5-6). The Corrupted Treant shoots frost in a 45-foot cone. Each creature in that area must make a DC 18 constitution saving throw, taking 14 (4d6) cold damage on a failed save, or half as much damage on a successful one.

Slam. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 16 (3d6 + 6) bludgeoning damage.

The Treant can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Treant regains spent legendary actions at the start of its turn.

Slam. The Treant uses slam.

Elemental blast (Costs 2 actions). The Treant uses Ice blast, Lightning blast, or Fire blast.

Animate trees (Costs 3 Actions). The Treant magically animates one or two trees it can see within 60 feet of it. These trees have the same statistics as a normal Treant, except they have intelligence and charisma scores of 1, they can't speak, and they have only the slam action option. An animated tree acts as an ally of the Corrupted Treant. The tree remains animate for 1 day or until it dies; until the Corrupted Treant dies or is more than 120 feet from the tree; or untill the Treant takes a bonus action to turn it back into an inanimate tree. The tree then takes root if possible.