Bug Bunny: Can be found in the second area of Pyrefly Forest.
Rare Bear: Can be found in the area past Mari’s picnic, by the waterfall. There is also a group of them down a trapdoor in Sweetheart’s garden.
Potted Plant: Can be found in the third area as well as in the area past Mari’s picnic.
Sprout Mole?: Can be found in the third area of Pyrefly Forest. It spawns inconsistently, so you may have to fight it a few times.
Ghost Bunny: Can be found in the secret area of Pyrefly Forest.
Note: The area cannot be re-entered once you leave.
To find the secret area:
Go to the right from here.
There’s a passage through the trees that leads to another area.
Once you’ve gotten to the end of said area, you should find yourself at a stump. Go to the right, through the trees.
You should be able to enter through here to get to the secret area.
OMORI – Optional Boss Locations Guide