That looks like it'll be really cute!! You're very creative!
The only thing I would say is that if it's for a baby, maybe don't use wool or yarn for the 'hair'... It might be better to make it 'solid' out of satin like the fins? (Does that make sense? Like something in one mass rather than stringy...)?
A first try on the body revealed the following: the tail is a nightmare to bag out and won't hold it's shape in the present state. It needs some kind of support (more than just batting) or to become broader (to accommodate more stuffing). Besides, being so curly, it is perhaps a tad too long to be safe for the baby...
I'll give it one more day of thought, but I might drop the plan altogether and buy something cute for her or make her an elephant instead.
I wonder if you could sew some zigzag trim (rick rack) really securely into the seam, to give a spiky effect? That would probably be more baby-safe than the yarn hair, and might look cute.
Cute! The curly tail seems like a great thing for a baby told hold/grab. Not sure how old the baby is, but my 3 month old is mesmerized by crinkle sounds. They sell the thin crinkle plastic for baby and dog toys that you could add as a layer inside.
That looks great! I think the really curly tail would be very interesting for a baby (you can pull it sideways but not uncurl it).
For the spikes maybe get some pleather or plastic-y material? That should hold the shape and add another interesting texture. Also replace single spikes with a zigzag shape, like the dinausors.