Walking Forest

Crushing Trunk. These large tree trunk like legs plant them selves in the ground firmly while they walk any creature that the walking forest walks through must make a DC 16 dexterity saving throw on a failure the creature is [condition]prone[condition effect], and suffer 1d6+5 bludgeoning damage, if they succeed nothing happens. 

Tall as an oak. The walking forest is hardy and mobile. Opportunity attack based on the walking forest moving away are retreated as the creature being resistant to that damage.

Hidden Horrors. While the walking forest is motionless within tree line or within 10 feet of two or more walking forest, it is indistinguishable from a collection of trees.

Multiple Legs. The walking forest has 8 legs. While it has more than 3 legs, the walking forest has advantage on saving throws against being  grappled, restrained, or being knock prone.

Idk, tracking slashing damage separate might get annoying as a DM. Up to you how you want to do that.

Many-Legged Assault The Walking Forest has 8 legs. Whenever it takes the Attack action, it can make a number of attacks equal to half its remaining amount of legs, rounded up. If it takes ten or more slashing damage from a single attack, it loose one leg.

Multi attack. Up to half is legs rounded up in attacks from its trunk legs, or one with its spit.

Trunk legs. Melee Weapon Attack: +8 to hit, reach 15ft., one target. Hit:  9 (1d6 + 5) [bludgeoning] damage. 

Spit . RangedWeapon Attack: +5 to hit, range 20/40 ft., one target. Hit: 9 (1d12+ 2) [acid] damage, while the target is hit it must succeed a strength saving throw of 14 or be  restrained [condition].