Tobias, Artifact Calamity

Cascade, Cascade, Wither
Tobias, Artifact Calamity's power and toughness
are equal to the number of artifact permanents
you control and artifacts in your graveyard.
When this card deals combat damage to a player
exile the top card of their library. You may play
cards exiled this way and use mana as if it
was mana of any colour to cast them.