Up for sale is the mana-swapping Deep Water, a common card from The Dark expansion of Magic: the Gathering. This is the original, black-bordered, English version.
Dep Water: Enchantment; spend U, then until end of turn, if you tap a Land you control for mana, it produces U instead of any other type and amount; casting cost UU.
These cards are all in at least Very Fine condition, with most being in unplayed, Mint/Near Mint condition.