Archtree

Poison Absorption. Whenever the archtree is subjected to poison damage, it takes no damage and regains a number of hit points equal to the poison damage dealt.

False Appearance. If the archtree is motionless at the start of combat, it has advantage on its initiative roll. Moreover, if a creature hasn’t observed the archtree move or act it is indistinguishable from a normal tree.

Heavily Rooted. The archtree’s movement is 0 while rooted. A druid can expend a 5th level spell slot to give the archtree a walking speed of 10 ft while the spell slot is expended. (When the druid regains its spell slots from a long rest the slot is no longer expended)

Create Seed. At dawn the archtree creates a seed. If planted it blooms into a 5 petal flower, and as an action can be picked. The flower lasts until the next dawn. A creature may remove one petal to cast the cure wounds spell, two petals to cast pass without trace, or three petals to cast plant growth or speak with plants. Alternatively, the planted seed may grow into a substitute tree. A substitute tree acts like a copy of this creature except it is only large size and has 1/2 the hit points.

Create Feysentinel. The archtree creates a large flower that takes seven days to mature and bloom. At dawn, if the archtree has no feyling, then a Feyling (Homebrew Monster) may sprout from this enormous flower if it has bloomed. The flower withers once the Feysentinel has sprouted and a new bud begins to form, it can only produce one such flower at a time. The Feysentinel must wait seven days once a Feysentinel has sprouted from it to sprout another, and it can only do so then if it has no living Feysentinel bound to it. The Feysentinel acts as a hive mind with the archtree and speaks on behalf of the archtree. The Feyling and Archtree also share their vision with each other.

Unusual Creature. An Archtree cannot attune to items. (Feysentinal can)

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

Multiattack. The archtree makes two slam attacks. If both attacks hit a Medium or smaller target, the target is grappled (escape DC 17), and the archtree uses its Woodification on it.

Slam. Melee Weapon Attack: +10 to hit, reach 5 ft., 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.

Woodification. The sapling roots a Medium or smaller creature grappled by it. The rooted target must succeed on a DC 17 Constitution saving throw. If the saving throw fails by 5 or more, the creature is instantly petrified. Otherwise, a creature that fails the save begins to turn to wood and is restrained. The restrained creature must repeat the saving throw at the end of its next turn, becoming petrified on a failure or ending the effect on a success. The petrification lasts until the creature is freed by the greater restoration spell or other magic.