Defense Grid
Artifact
Each spell costs 
more to cast except during its controller's turn.
"Woven together, strands of aether can form a mesh of surprising stability, though such a network tends to pull power from nearby devices." — Consulate engineer's log
Illustrated by
Kaladesh Inventions#34MythicEnglishLegality
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.