Block Tree
The Block Tree is a Darkner from Card Kingdom in Chapter 1. It can only be encountered in Forest.
The Block Tree resembles Card Kingdom's trees, but with a pair of legs and one single eye. It is shown bobbing up and down while looking around the area.
The Block Tree is hidden within the Dark Ponman rotation puzzle, which has a diamond chain rotating around the middle. A regular tree obstructs the path to the next room until a hidden switch in the Block Tree is pressed.
If the party rotates around the center for a while, the room darkens and eventually reveals the Block Tree at the north end of the area. Interacting with it causes both the Darkner and the obstructing tree to disappear.
Alternatively, if the Block Tree's hidden switch is hit before going around the center of the room, Ralsei becomes impressed with Kris and compliments them for discovering the switch's hidden location.[1]
- ↑
How'd you know that was there, Kris?
— Ralsei, Chapter 1
You're really amazing, you know that, Kris...? - ↑ UNDERTALE 6th Anniversary So We Play DELTARUNE Chapter 1 For Some Reason - LIVE! (01:49:49) on YouTube