I wanted it to be more of a Containment Priest effect where it denied my opponent the trigger, and on top gave it to me
Even 1 damage dealt to a creature from a source with deathtouch is considered lethal damage
If you have a lot of relevant permanents such that their Detention Spheres always have targets but yours might rarely have non Detention Sphere targets, you might need Banishing Light so that you can remove their Detention Spheres with a card that would otherwise be dead, having no other target than Detention Sphere
Actually, Un-sets are probably the single weirdest Magic product on the market, filled with silver-bordered cards that aren't legal for tournament play and brimming with obscure references and inside jokes
Unless otherwise indicated in the Event description or Promotions page, Event Reward ICRs are either uncommon or rare standard-legal cards*.
Also, sidenote: since that red mana is in the reminder text for Azula, she is still a mono-black spell