There's a way to do it without have many work. I need a tail that swings with the moviment of the body.

You should ask this question on www.elysiun.com, since this is a developers forum.

a way how to do the tail is to make emptys which are parented to each other, and give them a time offset against their parent, i tried it, the results aren't best, but you can use it...

there is no direct tail expression.
however you could use softbodies for this
or you use python to control the bones in
the tail in conjunction to the full bodymovements.

claas

http://orange.blender.org/blog/the-alternative-cloth-method

essentially slow parents and mesh hooks, previous to mesh hooks this could've been done with armatures and various contraints [and lots of empties, slow parent has been around forever]