My suggestion would be to make sure you're working from reference. The anatomy doesn't look right on the first 2. The sea monster could look alright, depending on how it is further defined (but that will require lots of reference). Don't say you want to make new creatures, because that just doesn't fly. All fantasy creatures are based on creatures in reality, and the human eye can catch inconsistencies in anatomy and such, even if the person doesn't realize it. In all honesty, if you're not working from reference, it's a waste of time (unless you're really really rediculously good, but I've only seen a handful of people good enough for that).