...
There was no duration limit though, so maybe that will help.
There are a number of drawbacks to this card (that are probably clearer with the new writeup) that I think make it not OP, and also a really good candidate, IMO, for an "other" card. The drawbacks also hopefully make it fun, not just because they allow more varied play, but also because the ways that you might have to compensate for the drawbacks allow a lot of room expansion -- for example, more use of burrow, healing, damage reduction, or "stealth." It could be central to a series, which is sort of how I was thinking of it.
Other than lasting just one turn, the differences/drawbacks are:
- Attacking creatures are damaged whether or not they kill their target.
- Attacking creatures don't damage the opposing player.
The first drawback is interesting because it makes the defensive stats/skills of the attacking creatures very significant to the usefulness of the card. There are just a few spells currently in the game that emphasize creature defense -- Gravity Pull, Overdrive, and Pandemonium (unupped.) But this doesn't seem to be a significant enough influence on the meta-game to encourage players to use low attack/high hp cards. There are a number of creatures that are easily overshadowed because of this (*ahem* Cockatrice) that would be made more viable by the introduction of a card like Battleground, or just more accessible damage/CC cards.
The second drawback is interesting for a related reason: That when playing Battleground, it's not necessarily any better to do more damage. In the turn that Battleground is played, the only thing that matters is the amount of damage done to each creature up to their hp total, with no consideration for damage that goes beyond killing all creatures. Overkill has no effect, and extra creatures attacking has no effect. This means that a deck that includes this card or considers strategies meant to respond to it needs to consider the attack of all of its creatures as related to the defense of each creature on the board or potentially on the board -- not just "higher is better."
These drawbacks even open up tactical considerations for playstyle, not just deck design -- should you bless your 7/7 Pegasus again and go for the kill in two turns, or throw it on the Ray of Light so you can kill both Lava Golems and ensure victory later on? If you have a Battleground in your hand, you have different and unique, flexible, and intricate tactical options available -- while still maintaining the core gameplay and the "fire and forget" interface.