Contaminated ground

[beneivel]

Rules: Enchant land Enchanted land is a Swamp. Whenever enchanted land becomes tapped, its controller loses 2 life.

So if I'm playing black and opponent is playing red let's say, if I cast this on their mountain to make it a swamp, who then gets to tap the land...me or my opponent?

I'd hope that I then get to use their land as mine, but if I can't it seems like the card isn't very valuable.

[Danokozmo]

All the card is doing is making the mountain a swamp, not giving control over it to you, so your opponent would have to tap it.

[Shadowex3]

Unless stated otherwise on the card enchantments, equipments, and whatever they're attached to will all keep track of ownership seperately. You own the enchantment but he still owns the mountain.

[ScribNib]

Contaiminated Grounds can be fairly valuable, I use it to give an opponent a swamp and then hit them with copious amounts of swampwalk.