This rule card has many effects, but it is all about cards that weasel out of real combat. First off, the event Weasel Attack! (428/3rd) can not be played while Keep It on the Battlefield is in play.

This rule card effectively creates a seperate island of combat during battle. No cards in play but not in the combat (including most events, since events aren't technically cards involved in combat) can affect the battle. This includes playing Cataclysm! (99/1st) on an attacked realm, since this is a card outside of combat (Cataclysm!) affecting a card in the combat (the realm).

Also, cards involved in the combat can't affect cards outside of combat (making cards like Lyr of the Mists (23/PO) and Arrow of Slaying (200/4th) nearly worthless).

Finally, this also means that card that take effect after battle is completed, such as Assassins (221/4th) can only target cards inside combat (like the defeating champion).

This is very good for people who like to use cards like Iuz the Evil (167/3rd) or Flaming Fist (65/FR) during attacks; the attacked realm is often razed right after combat.

While this is best for Flaming Fist, Iuz suddenly is not good to defend with, since his loss would not raze a realm (unless you somehow switched combat to over an opponent's realm).

Overall, this tends to hurt avenging themes, and cards that play around outside of combat. With so many cards being affected, this rule card will find its way into many decks that like combat and a few that don't. With a little finesse, this rule card could work very well for a defensive deck.

Keep It on the Battlefield has no extra defenses, so it can be taken out like any other rule card with things like The Genie Bottle (436/3rd).