Phyrexian Exo-Chamber

Crew 4 (Tap any number of other untapped creatures
you control with total power 4 or greater: This
permanent becomes an artifact creature until end of
turn.)
When Phyrexian Exo-Chamber is crewed,
sacrifice the creature(s) that crewed it. Search
your library for a creature card with mana value
equal to the total mana value sacrificed plus 1.
You may cast that card without paying its
mana cost.