I don't have too much expirience in sculpting, but I have seen on videos i'ts seemingly easy to make smoth tentacles. But in my case what I get are ugly ditortions on ends. I tryed adding more verticies and using Multires modifier but it hardly helps. Is it just how snake hook works ?
You need to enable Dyntopo in the left panel, otherwise the tool will only displace geometry, until it gets horribly mangled and creates artifacts.
Dyntopo will generate new geometry on the fly, provided you don't move your mouse too fast it should create a smooth hook.
Don't forget to tweak the detail size if you think the generated geometry doesn't fit.
Also consider using the latest version if you can, there has been gigantic improvements since 2.79 in the sculpting area.