Morrigan/Phoenix synergy:
Morrigan Throw, Shadow Servant -> Healing Field, Teleport M, s.H + Dark Harmonizer, f.H, TK Trap L, f.H, TK Trap L, c.HS, sj.MMHS, tk.TK Shot L, dp.H
Builds 1.2 bars back and does ~580K. You get another Dark Harmonizer call right after the combo ends bringing you to to 1.5 bars, so unless you do something dumb this looks like a safe combo to perform off of Morrigan's throw when you have 5 bars of meter and don't want to risk losing Dark Phoenix. Of course, it also works if you have Dark Phoenix, and is then roughly meter neutral unless you want to end in Phoenix Rage, which does about 1 million damage all told.
I'm still looking for that Morrigan/Phoenix combo synergy that lets me use Astral Vision mid-combo somehow, even if it involves TACs, while remaining meter neutral. It must be out there!
Right off the top of my head, there's
Jormungandr, but I'd imagine Aulbath has the aquatic terror angle locked down pretty well. Which sucks because I feel like a Siren would be great.
Yeah, a Siren wouldn't have much going for her, but the Gorgon makes a lot of sense.