Warpstone

When Warpstone enters the battlefield, you may search your library for a land card, shuffle your library, then put that card on top of your library.
Spells you cast cost {1} less.
As the raw stuff of Chaos it is the ultimate magical
substance and greatly sought after by the followers of
Chaos. Warpstone can be refined by Skaven Grey
Seers into a grey powder, allowing it to be used in
more controlled ways.