You have some nice sprites here Aero. Hope you don't mind a bit of critique though. I'll try my best to be helpful.
The Marley sprites are real nice. The flaws I find aren't noticeable from afar. There are like two blue pixels on her left hand
. I'm not sure if the outlining is right. I think less black lines on the dress would be nice, but it's hard to say. I could be wrong, lately I've been getting a taste at softer and less dark borders, so it could be just me. I don't like the neck area, seems awkward, perhaps that blank line, or how the head looks very solid and the body looks pastel-like almost. I honestly can't decide if she looks better with or without the pokeball. Lastly I find her expression and face a tad too perky, I always imagined her a tad more serious and bummed out almost, being a goth type look after all.
On that new sprite you did, I'd have to say the gray does look better. The head has to be the thing that bothers me most. Seems almost like a balloon, a tad big and oddly round.
You're splicing shows some potential, but needs some work. Overall I'd say a better conversion of making the Pokemon into one thing. A few of yours you just can't feel that it's a combination f two things. The Mudkip with Omanytte feels like a Mudkip with a shell. The Rosellia I don't even know what you fused with, just seems like a weird Roselia. The Octillary and Bronzor doesn't quite transcend textures too well, metal doesn't match the tentacles. Also square and defined head doesn't match wavy tentacles. The last one looks reel nice, but the different colors throw it off. I think finding a nice way to make it all one color set could make it look real cool.
That's all I'll offer for you. I hope I haven't offended or anything. If I was able to help in some way though I'm happy.