Hidden Herd
Enchantment
When an opponent plays a nonbasic land, if this permanent is an enchantment, it becomes a 3/3 Beast creature.
イラスト：
The List#USG-262レア英語適正
裁定
2004年10月4日
When it turns into a creature, it is no longer an enchantment.
2004年10月4日
Does not trigger on lands put onto the battlefield by a spell or ability.
2008年8月1日
A noncreature permanent that turns into a creature can attack, and its 
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.