This spell costsless to cast for each instant and sorcery card in your graveyard.
4/18/2017 Cryptic Serpent’s ability doesn’t change its mana cost or converted mana cost. It just reduces the cost to cast the spell.
4/18/2017 A split card only counts once for Cryptic Serpent’s ability, even if it’s both an instant and a sorcery.
4/18/2017 Cryptic Serpent’s ability can’t reduce its cost to less than .