It's a good idea to make mention of which software you're working with, that makes it easier to make specific suggestions. It's also a good idea to post some shots of the wire frame and any concept art/photographs you're working from to give us a sense of what your final product will be.
You might want to take a look at references of how tails on bipedal characters work. Right now it looks like its coming right out of his anus whereas it should be coming from the tailbone.
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It's a good idea to make mention of which software you're working with, that makes it easier to make specific suggestions. It's also a good idea to post some shots of the wire frame and any concept art/photographs you're working from to give us a sense of what your final product will be.
Those spikes would probably be better off as separate pieces.