During the magic phase the Skaven player is dealt magic cards from the the Winds of Magic as normal, and may use them to power spells, cast Dispels, etc, as normal.

As well being able to use power cards, Skaven sorcerers can also use warpstone as a source of magic energy. A Skaven sorcerer may consume one or more pieces of warpstone before he casts a spell. Each piece of warpstone consumed acts exactly like a power card. In effect, the pieces of warpstone act as bonus power cards that the Skaven player can use throughout the game.

By consuming warpstone the Skaven release raw power to strengthen their magic. However there is a price to be paid. Not even the Skaven can eat warpstone without suffering its mutating effects. When a Skaven sorcerer uses warpstone, and before he casts the warpstone-powered spell, he must make a Warp Test. This test determines if the sorcerer survives eating the warpstone or whether he is overwhelmed by its magic and twisted into a Chaos Spawn.