Even if you just have a few mana sources up after casting it you can now tap them for triple mana to essentially give you another turn
Positive loyalty taps a creature, negative loyalty draws cards based on the number of tapped creatures an opponent controls (hello, mass tappers), and the emblem turns your maximum hand size infinite and (optionally) returns anything that hits your graveyard to your hand
If you have a 2/2, a 3/3, and a */4 which happens to be a 4/4 when triggering, and by resolution you have a 2/2, a 3/3, and the */4 now happens to be a 1/4, the coven ability will resolve
Im specifically looking at blue color identity , so cards with other mana pips in their rules text are disqualified
Lithoform Engine You can get a ton of extra value out of your deck with Lithoform Engine, since it boosts almost anything you put on the stack
Xantcha has always felt like a popular or topical general, to the degree that I was beside myself when my research uncovered that Xantcha is the fifteenth most popular Rakdos general