Here is Wither Skeleton Fully Articulated, This model is Fully articulated meaning every joint limb and head moves, To assemble Simply Push the arms into the Main body slowly and rotate clock wise, the legs and body are print in place, to release the legs simply grab them firmly and rotate them back and forward,
Print settings, Supports needed for the head and arms you don't need supports for the main body but you can manually place some between the ribs, make sure you don't generate automatic supports as this can make the legs fuse with the body.
Nozzle size 0.4mm, Layer height 0.2mm, Infill 20%, Print speed 100ms, Wall count 3