Treant

Treant CR: 9

Huge plant, chaotic good

Armor Class: 16 (natural armour)

Hit Points: 138 12d12+60

Speed: 30 ft

STR

23 +6

DEX

8 -1

CON

21 +5

INT

12 +1

WIS

16 +3

CHA

12 +1

Damage Vulnerabilities: Fire

Damage Resistances: Bludgeoning, Piercing

Senses: passive Perception 13

Languages: Common, Druidic, Elvish, Sylvan

Challenge Rating: 9

False Appearance. While the treant remains motionless, it is indistinguishable from normal trees.
Siege Monster. The treant deals double damage to objects and structures.

Actions

Multiattack. The treant makes two slam attacks.
Slam. Melee Weapon Attack +10 to hit, reach 5ft, one target. Hit 16 3d6+6 bludgeoning damage.
Rock. Ranged Weapon Attack +10 to hit, range 60/180 ft, one target. Hit 28 4d10+6 bludgeoning damage.
Animate Trees (1/Day). The treant magically one or two trees it can see within 60 feet of it. These trees have the same statistics as the treant, except they have Intelligence and Charisma scores of 1, they can't speak, and they only have the slam action option. An animated tree acts as an ally to the treant. The tree remains animate for 1 day or until it dies, until the treant dies or is more than 120 feet from the trees, or until the treant makes a bonus action to turn it back into an inanimate tree. The tree then takes root if possible.

Treants are sentient trees. Sometimes a tree, especially in sacred groves or other regions touched by divine power, starts to gain a semblance of of a spirit. Over the course of years, decades, even centuries this matures and the tree forms a full consciousness. When this happens, a treant is born. They are fully mobile, and can move from place to place, and are always on the lookout for others of their kind. When they find one, they will nurture it in it's early stages and help it to fully form.
Each treant has contacts in any good aligned creatures living in the area, and have contacts with druids, shamans, and the like. Each recognised that the older treants have been around far longer than most other species have.

Suggested Environments

Forests & jungles.