It refers to the idea that you can come back from an impossible position if you just believe (in the heart of the cards)
The original Donate in Urzas Destiny is the classic example, but weve also seen cards like Harmless Offering and Zedruu the Greathearted iterate on the concept
This makes a decent strategy to build around, as Gengar may cause a hiccup to the strategies of other decks - with cards such as Misty, Giovanni, Sabrina, Blaine, and more being affected
Going wide with your other creatures can whittle down your opponents life total, while Shelob, Child of Ungoliant can go for commander damage
If only one half is cast, the spell is the color of that half
High-value cards require extra scrutiny because they attract more sophisticated forgery attempts