Cheapest priced copy (The List): $1.29 at Card Kingdom, near mint, their price list as of .
Hidden Herd 
Enchantment · Rare · Urza's Saga · #262
When an opponent plays a nonbasic land, if this permanent is an enchantment, it becomes a 3/3 Beast creature.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $1.29 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The List | USG-262 | Rare | $1.29 | — |
| Urza's Saga | 262 | Rare | $1.29 | — |
3 rulings from Wizards of the Coast
- 4 October 2004When it turns into a creature, it is no longer an enchantment.
- 4 October 2004Does not trigger on lands put onto the battlefield by a spell or ability.
- 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.