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
Sadly, that's all we've got time for for now - there's wrapping paper to clear and leftovers to munch
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
If several decks in the Top 8 make prominent use of this powerful lady, the potential for a short term spike over $50 could trigger a good chance to sell
Void Mirror
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