Skeletons will die when attacking a Valkyrie's shield. To take advantage of this, select a location with multiple skeleton summoning stones. Back yourself into a corner and use an object to hold the [Shield] key or button. Allow the game to idle in this state as long as desired. Note: Use higher difficulty settings for faster respawns. A good location to find skeletons is World 1 level 2 or level 3. There are areas where two skeleton spawners spawn consecutively in room after room. Remain there and hold your position to kill them. Go to the Tomb III (Crypts of the Sun King III) and progress until the last stage. You will find two Liches here. Do not kill them; they summon will summon seven or eight Skeletons every thirteen seconds. They will eventually kill themselves or die on the spike trap. Retry as many times as desired.