Black Eggplant was the black eyefly.
He from Psycho Waluigi and waluigi turn very psychc.
When you kill Psycho Iris in snailiad 3 she will gave that eggplant then fly away.
That eggplant make you turn into a Legend snail.
There is a top secret area that yu can only go to at 10:00 PM- 6:00 AM where there is an open hole that you fall in to find a free eggplant.