They're powerful, flashy, and, for longtime fans of both games, pretty irresistible right now
The depth of the concave cut is dictated by the performer's skill and requirements
A few non-Standard sets and promos use the same symbol, but generally, the expansion symbol is great to make sure youre looking at the correct one and identify which set it comes from
Then all creatures are sacrificed by their controllers simultaneously
But the spell/creature side of these are more efficient than the average from the Zendikar Rising modal double-faced cards and the mono-colored ones can enter untapped if you pay life, so I think many will find a home, and not just in Goblin Charbelcher decks
The only requirement was that the artwork had to depict a white-aligned mage sacrificing themselves to cast the most epic protection spell. The exact nature of the spell wasnt specified, but it had to feel grand and powerful