First of all, it's not a quest. Second of all, no one can tell you (it's like when you had to find the Blue Magikarp, I think). ;)
Chat with our AI personalities
To find Missingno on Pokefarm, you must complete a quest.
by Getting certain things they tell you to get, and then you complete the quest.
you give moomoo 7 oran berries
As far as I know you can't, but there might be a quest or something where you can be a for a short period of time. There is a glitch that allows you to turn invisible. I ain't sure if it is fixed, but if you are really interested, try going to youtube.com, search for "sachiko nami", she did a video on how to do it. BUT if you mean the ghostly robes, which makes you supposedly invisible (it is more of semi-transparent), you need to do a quest "desert treasure" and etc.
this book is by carolyn keene and she is dead