Even the base printings of Gemstone Caverns are worth around $50, so no matter what, you'll be happy to open a copy, and very, very happy if you happen to open Gemstone Caverns #51.
Estimated value: $400 - $3,500 (depending on condition) Advertisement Time Vault can grant an extra turn
When the last [soul] counter is removed, sacrifice CARDNAME and return the exiled card to the battlefield
Its market shows a gentle upward trend, with a 6.23% increase all-time and steady gains in the past month
Being able to prevent flyers from blocking can be decent when aggressive, but it does do work in a pillow fort deck focusing on granting deathtouch
On an Unknown card, theres basically one route to joy, and thats to make them laugh