I have no idea whether the 'regenerate target enchantment' clause is worth it. I'd always forget it was an option, since it was so rare an event compared to regenerating creatures. Does that make the ability bad, because people forget it exists, and makes people feel bad when they could have used it/walked into it? Or is it good, because it gives hidden value, and makes players feel clever when it matters and they realize it? I have no idea...

Dunno, but it's an evil combo of "No really, I'm invulnerable, stop trying to break the lock, it won't work" with your Sphere enchantment.

Seems odd to see a white thrull.

White thrulls already exist, and I'm sure we'll be seeing a few more when we return to Ravnica.