Sibsig Muckdraggers

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.

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 ) is 6 even if you exile three cards to cast it.

You can’t exile cards to pay for the colored mana requirements of a spell with delve.

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.

Because delve isn’t an alternative cost, it can be used in conjunction with alternative costs.