Overclocked Dynamo

At the beginning of your end step, exile the top
X cards of your library, where X is the number
of instant and sorcery spell you cast this turn.
You may cast an instant or sorcery spell from
among the exiled cards without paying it's mana
cost.
"What, the turbine's crossing past redline? It's threatening to explode? Alright, what is there to be
worried about?"
-Ral Zarek