is this really Astaroth? i thought she had a spade point at the end of her tail, plus didn't she have black eyes, and non-rigid horns?

You're definitely right. Most telling is that the whites of Astaroth's eyes are black instead. Eyes are one of the most important character-identity traits, so there's no way an artist would have made that mistake if they wanted to draw Astaroth.

Removed the tag.

i thought so i didn't want to mess with it cause i wasn't too sure, since i don't keep up with the series really. i thought that it was possible she might have gone some sort of transformation or whatever.

This is Melfis. I think that's Shion and Astaroth over on the right, though.