To easily gain experience, you will need Level 255 mode, two Hierophant Rings, Rapidus Fio Glyph, Slash Attribute at 65,535, ability to kill Skeleton Hero upon impact with Rapidus Fio, and levels over 100. Go to the Skeleton Cave, and go to the hall on the middle floor with the large number of Skeleton Friskies in a row. Equip Rapidus Fio, two Hierophant rings, and any strength boosting equipment or Glyphs. Run from one end of the hall to the other, leaving and re-entering the room. Each pass through of the room will result in approximately 1,000 experience points, and for every minute you will gain approximately 23,000 experience points.