WotC person 1: "Hey, dragons don't really make sense in gothic (horror) world"
WotC person 2: "What about making their wings stained glass? That's in gothic (cathedrals)."
And thus we got the prettiest dragons in all the planes.
....anyway, Moonveil Regent looks sweet. I assume it's at least partially a plant for New Capenna's tricolor factions, but it also looks very abusable in the right deck. Seems very fun for any heavy-gold decks. Ramos, Dragon Engine multicolor tribal has been on my shortlist of deck ideas for a while, and this looks like a strong inclusion there.
As for other stuff....
- Horde Extermination looks excellent, and may be the new best board wipe in the format, at least from an efficiency standpoint. I guess it competes with Blasphemous Act, but it is a mana cheaper if BA hasn't maxed out its cost reduction.
- Spectral Adversary is interesting. The body is reasonable - a 2/1 flash flyer that can grow - and phasing stuff out allows for a lot of shenanigans, both offensive and defensive. I'm definitely expecting some shenanigans.
- Tainted Adversary, on the other hand, is a miss for me. Looks like it would be good in Standard, but in EDH, I think it compares poorly to other token producers.
- Fearless Adversary is... fine. Similar to Tainted Adversary, this looks more relevant for Standard - I'm not a big fan of anthems in my decks, and sticking it on a creature is just asking for a blowout when it gets killed.
- Celestus Sanctifier gets a callout because it is so rare for white to get self-mill and/or card selection. Otherwise, doesn't look that powerful.