So the idea with O-Zuijin is that it is a great warrior spirit. This is in contrast to the character of O-Kagachi from Kamigawa block. So, while I'm not suggesting that this O-Zuijin has a place of importance similar to O-Kagachi, I'm trying to reinforce the idea that this is a major spirit. That said, from a flavor standpoint, I should probably make it mythic. But the ability as it exists makes it feel more like a rare. So we'll see how I juggle all that as the set develops.
...and now you have to define "regeneration shield."
Section 701.12 of the CR, "Regenerate", has three subsections. (a) deals with activated abilities, triggered abilities, and spells. (b) deals with static abilities. (c) is the only subsection that uses the phrase "regeneration shield":
701.12c Neither activating an ability that creates a regeneration shield nor casting a spell that creates a regeneration shield is the same as regenerating a permanent. Effects that say that a permanent can't be regenerated don't prevent such abilities from being activated or such spells from being cast; rather, they prevent regeneration shields from having any effect.
Notably, it's unclear whether cards like Knight of the Holy Nimbus and Mossbridge Troll actually count as having a "regeneration shield" on them. The relevant Gatherer rulings contain the phrase "The [static] ability essentially means that CARDNAME always has a regeneration shield," but don't confirm that it actually does. (And Gatherer doesn't = rules anyway.)
I think "regeneration shield" is rules-supported, but it could use more clarity. For Knight of the Holy Nimbus / Clergy of the Holy Nimbus / Mossbridge Troll, the "shield" couldn't possibly exist unless the replacement effect created it. But since they're using "shield" colloquially / casually, yeah, they haven't bothered to define how the "shield" works with static abilities like this.
Really, what those cards should read is, "If ~NAME~ would be destroyed, instead regenerate it, then destroy it." Or even better, "If ~NAME~ would be destroyed, instead put a regeneration shield on it, then destroy it."
:symb:: Put a regeneration counter on Drudge Skeletons. (If a creature with a regeneration counter on it would be destroyed, it isn't. Instead tap it, remove all damage from it, remove it from combat, and remove the counter. Remove the counter at end of turn.)