In order for us to even consider breaking a rule, we have to first have a card that seems cool and feels right yet somehow still breaks a rule
For Final Fantasy XII, Vaynes Treachery joins Overkill as our main source of interaction, and is complemented by Zenos yae Galvus and Sephiroth, Planets Heir and with so many removals and black spells on the list, The Darkness Crystal seems like a great choice
Although it remains to be seen just how impactful this card will be in terms of gameplay, this card might nonetheless see use as the centerpiece of a gimmicky, off-meta deck
To reiterate what others have said, I think the art/price proposition is really good
Spoilers: At the end of the Tarkir: Dragonstorm story, it was revealed that Jace visited Ugin and Bolas in the Meditation Realm, and the events there made the whole realm break into fragments
Other abilities that interact with life gain or life loss will interact with this effect accordingly