2014-11-24 : Because delve isn’t an alternative cost, it can be used in conjunction with alternative costs.

2014-11-24 : Delve doesn’t change a spell’s mana cost or converted mana cost. For example, the converted mana cost of Tasigur’s Cruelty (with mana cost {5}{B}) is 6 even if you exile three cards to cast it.

2014-11-24 : You can’t exile cards to pay for the colored mana requirements of a spell with delve.

2014-11-24 : You can’t exile more cards than the generic mana requirement of a spell with delve. For example, you can’t exile more than five cards from your graveyard to cast Tasigur’s Cruelty.

2014-11-24 : You exile cards from your graveyard at the same time you pay the spell’s cost. Exiling a card this way is simply another way to pay that cost.