Defense Grid
Artifact
Each spell costs 
more to cast except during its controller's turn.
"Properly installed, each powerstone emits a targeted electromagnetic field that halts momentum as sure as stone." —*Tome of Obstructions*
Illustrated by
The Brothers' War Retro Artifacts#76zRareEnglishLegality
Rulings
Oct 4, 2004
The additional cost can be reduced by effects that reduce costs, such as Sapphire Medallion.
May 1, 2006
In Two-Headed Giant, spells don’t cost extra on your own turn.