Blacks Crystal offers some rather unique effects that could go in a variety of different decks, but unlike some of the other Crystals, this doesnt really create any exponential value
Hold on to Prince Eric, Seafaring Prince to keep her safe, and plenty of the healing cards like Healing Glow and Julieta Madrigal, Excellent Cook , and you should be able to keep Isabela in play long enough to get you the win
Even very controlling 18-land decks can just be 18 lands plus several cards that draw or fetch lands for you (Cultivate, Field Trip, Pop Quiz with access to Environmental Sciences, etc.) and skip the 19th land
It allows you to respond to your opponent's strategy and keep the game under your control
I've learned long ago, though, that the key to flavor is not always hitting the nail on the head
The impact it will have on Tron, Affinity, Eldrazi Aggro, and various Ensnaring Bridge decks is huge