Arboreal Curse

This curse turn the target into wood. If the target’s body is made of flesh, the creature must make a Constitution saving throw. On a failed save, it is restrained as its flesh begins into bark. On a successful save, the creature isn't affected.

Stage 3

A creature restrained by this curse must make another Constitution saving throw at the end of each of its turns. If it successfully saves against this spell three times, the spell ends. If it fails its saves three times, it is turned into a tree and subjected to the petrified condition for the duration. The successes and failures don't need to be consecutive; keep track of both until the target collects three of a kind.
If the creature is physically burned, chopped down, or otherwise destroyed while petrified, the creature is slain.
A creature remains transformed unless the effect is reversed within one year with remove curse, wish, or similar magical effects. If the creature spends one year and a day as a tree, the transformation becomes permanent, and nothing can return the creature to its original form.