Cheapest priced copy (Adventures in the Forgotten Realms): $2.49 at Card Kingdom, near mint, their price list as of .
Mordenkainen 
Legendary Planeswalker — Mordenkainen · Mythic · Adventures in the Forgotten Realms · #283
+2: Draw two cards, then put a card from your hand on the bottom of your library.
−2: Create a blue Dog Illusion creature token with "This token's power and toughness are each equal to twice the number of cards in your hand."
−10: Exchange your hand and library, then shuffle. You get an emblem with "You have no maximum hand size."
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $2.49 to $27.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Adventures in the Forgotten Realms | 64 | Mythic | $2.49 | $2.99 |
| Adventures in the Forgotten Realms | 283 | Mythic | $3.99 | $3.49 |
| Adventures in the Forgotten Realms Promos | 64a | Mythic | — | $27.99 |
| Adventures in the Forgotten Realms Promos | 64p | Mythic | $9.99 | $12.99 |
| Adventures in the Forgotten Realms Promos | 64s | Mythic | — | $3.49 |
2 rulings from Wizards of the Coast
- 23 July 2021The cards put into your hand due to Mordenkainen's last ability aren't "drawn." Anything that cares about you drawing cards won't notice your hand suddenly becoming very, very well-stocked.
- 23 July 2021The power and toughness of the Dog Illusion token will change as the number of cards in your hand changes.