Cheapest priced copy (Strixhaven: School of Mages Promos): $0.99 at Card Kingdom, near mint, their price list as of .
Harness Infinity 
Instant · Mythic · Strixhaven: School of Mages Promos · #191p
Exchange your hand and graveyard.
Exile Harness Infinity.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.99 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Strixhaven: School of Mages Promos | 191p | Mythic | $0.99 | $0.99 |
| Strixhaven: School of Mages Promos | 191s | Mythic | — | $1.49 |
| Strixhaven: School of Mages | 191 | Mythic | $0.99 | $0.99 |
| Strixhaven: School of Mages | 343 | Mythic | $0.99 | $0.99 |
3 rulings from Wizards of the Coast
- 16 April 2021If either your graveyard or your hand has no cards in it, the exchange still happens. If one of those zones has any cards in it, you will move them to the other zone.
- 16 April 2021If you have more cards in hand than your maximum hand size (usually seven) during the cleanup step of your turn, you will need to discard cards down to your maximum hand size.
- 16 April 2021Cards put into your graveyard this way are not discarded. Any ability that triggers when you discard a card will not trigger.