Spells and magical items cannot be used by a champion attacking the Battle-Fens. Spells and magical items used by defenders of this realm are doubled in level.
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TSR
Wizards of the Coast
If your deck relies on spells or magical items, the Battle-Fens is a great realm to use. All attackers within this Birthright realm are prohibited from using magic or spells. Consequently, no offensive or defensive spells or magical items can be used when attacking this realm. It simply does not work if a spell or magic item is already attached to the attacking champion. In response to such cards as the Loup-Garou (236/4th), an attacker cannot play spells or magical items once combat has begun.
Furthermore, all spells and magical items used by the defenders are doubled in level by the Battle-Fens. A level bonus can only be applied to spells and magical items that have this doubling. This ability does not affect cards like The Necklace (176/4th) or Reverse Gravity (385/4th). Champion cards that can cast spells and magical items with high bonuses are good choices for defending the Battle-Fens, such as the Girdle of Storm Giant Strength (183/4th) or Libram of Ineffable Damnation (8/BR-chase). Bengoukee the Witch Doctor (434/3rd) is the best champion to use if casting spells to defend the Battle-Fens, since his spells are multiplied by four now.
These restrictions and bonuses also apply to those helping the attacker or defender, if the optional Aiding the Attacker or Defender rule is used.