The volatility of collectibles, including Pokmon cards, introduces the risk of fluctuating values
You also have the option to not untap it, which lets you keep control of the creature
Related What can NOT be transferred to TCG Live Cards from the HeartGold & Soul Silver series Avatar items Unopened Products Specific Coins, Card Sleeves, and Deck Boxes (unknown which ones at the time of writing) In-Game Currency Friends List Saved Deck Lists However, players can export from TCG Online and save lists locally so they can import them to TCG Live If you do not wish to open your unopened products before the migration, you can allow TCG live to convert them to a set number of crystals
I developed those thoughts through because Mentor is my favorite (non-evergreen) combat keyword of all time
The most popular cards from the set were Fable of the Mirror-Breaker of Kiki-Kiki, Boseiju, Who Endures, and the new Magic planeswalker, The Wandering Emperor