I just discovered two ghost stamp pikachus in my collection.
I honestly thought it was Shadowless, but noticed as I was grading that it’s the ghost stamp.
From the small amount of info i found, it seems fairly well known and not a rare error.
How rare is it? Mine are in maybe PSA 8 shape. I normally only grade PSA 9 and above, but i might make an exception if it’s worthwhile to get them encapsulated.
Thank you.
Well the last one sold for $90.89 at auction.
I think it’s worth grading IMO. If you plan on keeping them long term, I would definitely get them encapsulated. One of your copies might earn a 9, you never know. 
Some of the guys here can correct me if I’m wrong, but while it’s well known it’s not a common error. I’d put it in the same category as something like No Damage Ninetales or No Stage Blastoise,etc… Plus it’s a Pikachu. It’s a very desirable card. In PSA 10, you’d probably looking at $600-1000.
Thanks for this info. I’d never really known about it and I thought maybe it was a fake stamp erased at first pass haha
From what I heard they usually came in Theme Decks, Zap if I recall correctly. I’m not aware of any copies found in booster packs. It’s probably more rare than you think.
Some more info:
Ghost Pikachu Confirmed