Wither Skeleton Tweaks makes farming and searching for wither skeletons a much easier task. Vanilla's method of farming skulls is frustrating at best, and I believe I can do better.
Wither Skull Fragments
Any wither skeleton that does not drop a Wither Skeleton Skull will drop a Wither Skull Fragment.
Any skeleton that spawns in the nether will be converted to a Wither Skeleton. They will retain their original weapons, so converted Skeletons will have bows.
Damaged Stone Swords and Bows are removed from the drop tables of all skeleton-based creatures, including Wither Skeletons, Skeletons, and Strays.
Wither Skeleton Tweaks also adds the Immolation Blade, a sword which causes instant death and beheading for all skeleton-based creatures. There are two variants that only differ in texture.