COM: Angela Falix Underwater

Okay, so first of all, and just to get this off my chest so I don't let it affect the rest of the critique, I don't think you should use bases for commissions. In fact, I don't think people should use bases at all--I happen to be very against the use of bases in general. I also would like to point out that you should not use backgrounds that you yourself have not created for commission work since you could run into problems regarding copyright down the road--though admittedly, I don't use VK so I'm unaware of what the specific copyright terms are for the images featured.
That said, I'll not be letting my base-bias influence what I say for this critique, but it does mean that I won't be able to comment on anatomy or anything pertaining to the original base. I'll only be making note of the colours, textures, technique, background and how everything meshes together.
Onto the critique:

Right off the bat there's a jarring disconnect between the colouring of the foreground character versus the background. There's no colour blend. It looks rather just like an image of a doll layered over an ocean background. If that was the intent then fine, mission accomplished, but if the intent was to make the character look as though they're actually swimming through the ocean, then I'm afraid this image doesn't capture that at all. Truthfully it looks far too staged and static, and considering all art pieces are static images, it's important to try and avoid that--to make them come to life and pop.
You've got an even consistency in the line art, which is very good. I looked over the original base-poster's DA and can see that most, if not all of their bases, are naked images, so I imagine the clothes, fabrics and hair are all your doing. If so, you've kept the line art consistent and have used the perpetual thickness of the lines in order to create folds in the fabrics or curves in the hair which don't reflect negatively on the piece.
Frankly the piece is a little... glittery for my tastes, but I understand that this is a Winx Club sort of piece and that tends to be the style, so good job in mimicking that.
There is, unfortunately, no consistency to the shadows and lighting. When looking at the character's body, the light source looks as though it's coming from the character's left [picture right], but the pink part of the tail as well as the hair makes it look as though the light source is coming from above. In fact, the tail is shaded in a way that indicates that there is no light source coming from the picture's right, which directly conflicts with the shading and highlights on the character's upper body. Ideally one should determine where the light source should be coming from first and lay out their shadows and highlights accordingly based on that decision. I would also recommend looking into underwater colouring tutorials, since the ripples on top of the water in ocean/lake/underwater scenarios tend to create unusual swathes of light and shadow.
Regarding the hair and fabrics, I'm unaware as to whether the character is meant to be moving or is, in fact, stationary. The fabrics give off the idea that she's stationary underwater with how they seem to float around her, but if that's the case then the hair should be reacting in a similar way, rather than entirely connected behind her as it is.
All in all the piece is okay, but there are some physics problems that are unique to underwater situations and perhaps too much of a disconnect between the foreground and the background.
That's all I can offer up at the moment.
Hope it was helpful.