Converting Sprites into other formats is a great help.
Say you want to have Hexen's Korax Or Doom's Imp but you want to have them in Heretic you can use a tool known asto convert sprites quite easily.
To use this tool first you must get sprites from a wad (e.g Doom.wad) when you have exported them using your wad or lump management tool (preferably SLumpEd) but have them exported into two formats .lmp and .png.
Then boot up DoomPicDump.
Navigate to your sprite folder select and modify the input to match the extensions e.g if you saved the files as .png change it to .PNG.
Then modify any settings you want and click convert all the newly created png files are ready to be imported to your wad.