Retroactively figuring out a DM move

[Nettlekid]

So in my most recent session, in a campaign largely involving a plot by Vampires to control most of the world with Necrotic Cysts, I had a Dragon raging against trespassing PCs before being muted and rendered docile by the bad guy using Necrotic Domination. Except that upon rereading Necrotic Domination later, I realize it only works on Humanoids (all the other Necrotic spells just say "living creature," so I thought this one did too.) Now, as a DM I could just say this is a powered up world where it works on anything, but I hate bending the rules like that. Can anyone think of a way that the BBEG could have forced the dragon to sit down and shut up for the time being, that would have looked like mind-breaking in some way or another? The bad guys involved had 6th level Powers and if need be, a small selection of up to 6th level arcane spells too, so if there's a spell or power that would feasibly stop a Dragon, preferably without a save (since I'd hate to fudge that roll), that would be awesome. So far I'm leaning toward Brain Lock and having had the bad guy keep manifesting it again and again until the Dragon got a Nat 1 before making his entrance, but better solutions are probably out there.

[Khatoblepas]

If you've already got a Necrotic Cyst inside the dragon, a scroll of Necrotic Tumor will dominate the dragon with no save*. You are limited to a single suggestion if they succeed, but "Sit there like a good dog until I have finished and am safely out of the way." is valid.

*Okay, there is a save, but it's mostly a formality about whether the spell will be permanent or have a lesser effect.

[Nettlekid]

If you've already got a Necrotic Cyst inside the dragon, a scroll of Necrotic Tumor will dominate the dragon with no save*. You are limited to a single suggestion if they succeed, but "Sit there like a good dog until I have finished and am safely out of the way." is valid.

*Okay, there is a save, but it's mostly a formality about whether the spell will be permanent or have a lesser effect.

Absolutely perfect. The effect wore off when the party tried to take the Dragon's hoard, and I based that on that a dominated creature will mentally fight to prevent something that goes against its very nature, and I think that'll do just fine. Thanks!