At the beginning of your upkeep, choose target opponent. Until end of turn that player can't cast spells, you may look at the top card of their library any time, you may play the top card of their library, and you may spend mana as though it were mana of any color to cast spells this way.

Poor Unfortunate Souls - {X}{B/P}{U/B}{U/B}: Become a copy of target legendary creature with mana value X, and then return that creature to it's owner's hand. Transform Ursula, The Sea Witch.

(Vanessa, Bride to Be has all triggered abilities of Ursula, The Sea Witch and all abilities of targeted legendary creature. Vanessa, Bride to Be has power and toughness of targeted legendary creature)

When Vanessa, Bride to Be enters the battlefield, seek Nautilus Necklace and attach it to Vanessa, Bride to Be.

If Nautilus Necklace is destroyed, sacrifice Vanessa, Bride to Be. When this happens, you may mill half your library to seek Ursula, Ruler of All the Ocean and put it onto the battlefield tapped.