Which Diantha do you have?
Same name, 32× the price: $1.18 to $38 raw. The difference is printed on the card — it is just not somewhere most people think to look.
Forbidden Light Japanese · #101
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$38
69% gem
GX Ultra Shiny · #129
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$3.95
no PSA data
Tag Team GX All Stars · #148
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$2.75
33% gem
Forbidden Light · #105
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$2.54
7.1% gem
Forbidden Light Japanese · #086
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$2.33
70% gem
GX Starter Decks · #117
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$1.18
no PSA data
We have no hand-checked note for these printings yet, so the guidance above is the general rule rather than something specific to this card.
Prices are raw market value. Click a printing for its full grading verdict — the gem rate, the fees and whether it beats selling raw.