To get gengar:

1) Go to eterna forest.

2) Go into the old chateu.

3) Go to the dining room and follow the ghost until you can't find him.

4) Exit the dining room.

5) Go upstairs into the middle door.

6) Go into the first room on the right.

7) Talk to the girl and she will dissapear.

8) Get out the the room.

9) Go to the second room on the right.

10) Click on the picture with the flashing eyes.

11) Move around the room until you find a gengar.