Unless you're talking about a different move, the attack you're talking about doesn't require low health. I haven't quite figured it out myself, but I think it either involves the overall amount of power you use during a match or the time spent fighting.

Even though it's a nice simple character, most of her attacks are pretty generic aside from her level 3 and secret move. I was really hoping to see the author implement some of the attacks that was mentioned in the production notes of the anime where Sayaka's sword was actually retractable (like a whip sword) and that it could be rigged to explode.

Oh and her AI is brutal. I hate that too.

I lamented the lack of a readily available and up to date Arceuid Brunestud for Mugen, and that Arc is often overlooked in favour of other Melty Blood characters.

Jesuszilla corrected me by referring to Michael Roa Valdamjong, a playable character in Melty Blood Actress Again who as far as I'm aware doesn't have a Mugen character.  Legendary Blue Shirt is a Roa player.

I dismissed his amendment, claiming that Michael Roa Valdamjong is a masculinity-challenged individual that would look more at home in a yaoi doujin than in a Mugen engine.

Hope that cleared things up for you.