User:Stern
From The Battle for Wesnoth Wiki
Animation Tutorial: Blocking
Learn how to take a standing base frame: 
To full animation: 
Through "animation blocking."
For this tutorial, you will need:
A base frame of the unit -> (http://wiki.wesnoth.org/Creating_a_scratch_built_sprite)
A graphics editing program -> http://www.gimp.org/
Lets get started
The first step of blocking is to divide the moving parts of your character's base frame into easy to distinguish colors. For example, I recolored the Ghast's arms, legs, heads etc.
Credits
Zerovirus for Ghast baseframe.