Mefican, The Silver Tongued

As long as a nonland card in an opponent's hand
is revealed or a nonland card is exiled by an effect
you control, you may cast that card and spend
mana as though it were mana of any colour to cast
it. When you cast a spell this way, exile it at the
beginning of the next end step, then return it to
it's owners hand. If you cast a creature spell this
way, it gains haste.