[Fern]

Demon Breaker Dullahan?

I forgot Dullahan existed... maybe the Demon Breaker momentum effect could be changed to "your first stance change in the round" rather than "the first time a stance has been used that round" if Dullahan would be too bonkers with it.

Thinking about it, it might be a lot of FP burn out because of Dullahans losing FP from any action they take no matter the momentum cost. If it's a 30 SAN one that should be 3% FP per action, and if they have about 250 FP, that should be about 7 FP cost per.

So, popping Demon Break off to begin with costs 10% FP, in that case it'd be 25 FP for the activation. Soul Rage is another 7 FP, and on round tick it's another 25. If they go through four stances next round, that's another 28 FP...

This leaves the hypothetical Dullahan at 165/250 FP, how much FP they consume after that depends on what buttons they press but I think it sounds like they'd empty out pretty fast, so maybe it'd be okay? Dullahans building way more FP generally won't be tanky since they have to build hit rate either way...

Chaser, Rising Tide and Elemental Rave would be roughly 16/11/11 FP costs before Dullahan racial, and with the racial they would be 23/18/18. I think rather than busted, it might seem like a meme build more than anything because of how much FP the Dullahan would be burning. But if it were an issue, it could just have the alternate condition mentioned earlier instead!
 
EDIT: I tried building a mainland BK/DH Dullahan with whatever weapon, assumed Mayelia, Dragon King Glove and Helmet, Mars Badge and whatever boots. It doesn't look very tanky IMO, but it could probably slap before running out of FP. Kinda hungry for skill slots, though, but that could be alleviated a little bit by removing some DEF/STR/VIT and throwing it into GUI for an extra slot. Probably worth noting that in this hypothetical build, the Dullahan loses 10 FP with any action taken.