Battlefields are special cards - They are spells.
Only one Battlefield can be active at once and they affect both player!
If a second Battlefield is played the first one will get destroyed.
(The background where you play cards will change it look.)
Some Neutral Battlefields ->
Some Class Battlefields ->
Some Battlefield Minions ->
Shaman of the Earthen Ring:
The white shark:
Here is one more weapon for you ->
Now Blizzard can add each location, each forest, each town… Each dungeon and raid as Battlefield card with very cool effects.
Maybe a higher trust level can post this pictures so you dont have click on each link.