The Flying plant is a pet that can be obtained. To get him you must fertilize all the dead plants in the Gardens. You need the fertilizer, which you can find by going south one screen, then east one screen, starting from outside the door of where you recieved the quest. In this area there will be a large flashing sign shaped like a pile a dung. Go down the ladder next to the door, and then hit the wall to the left, destroying the Hidden Door. The fertilizer is through the brown door.
The Flying Plant will only have half it's health bar filled when called. It drains enemies health, filling it's own health bar in the process. When it's health bar is full, and you are injured, it will heal you with it's own health.