Pokemon card errors used to happen quite a lot, but later they started to stop misprints and the old misprints value shot to around 20$-30000$. They don't really make mistakes anymore but now they do have some quite some mis cuts. These card errors would either be fixed later or they would try to throw out as many mistakes as possible, but some would leak for a lot of money. You can post a picture or comment about some misprints or mis cuts.

Here, the icon on diglett's move "Dig" is turned sideways. It is worth around 21$

Pikachu misprint

Here, the stamp that says pokemon is on the attack "Thunderbolt" flipped over when it is supposed to be in the top right corner. This cards worth is in the thousands.