Cheapest priced copy (Betrayers of Kamigawa): $0.35 at Card Kingdom, near mint, their price list as of .
Genju of the Fens 
Enchantment — Aura · Uncommon · Betrayers of Kamigawa · #66
Enchant Swamp
{2}: Until end of turn, enchanted Swamp becomes a 2/2 black Spirit creature with "{B}: This creature gets +1/+1 until end of turn." It's still a land.
When enchanted Swamp is put into a graveyard, you may return this card from your graveyard to your hand.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
4 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Betrayers of Kamigawa | 66 | Uncommon | $0.35 | $0.49 |
| Duel Decks: Garruk vs. Liliana | 47 | Uncommon | $0.35 | — |
| Duel Decks Anthology: Garruk vs. Liliana | 47 | Uncommon | $0.35 | — |
| The List | DDD-47 | Uncommon | $0.35 | — |
2 rulings from Wizards of the Coast
- 1 August 2008A noncreature permanent that turns into a creature can attack, and its {T} abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn't matter how long the permanent has been a creature.
- 1 October 2009Activating the ability that turns it into a creature while it's already a creature will override any effects that set its power and/or toughness to a specific number. However, any effect that raises or lowers power and/or toughness (such as the effect created by Giant Growth, Glorious Anthem, or a +1/+1 counter) will continue to apply.