Tier 1: Basic Humans. Minimally trained. Think a bar fight or back-alley brawl.
Tier 2: Trained Warriors. Skilled and equipped with weapons. Think Samurai or Grunt Soldiers
Tier 3: Elite Fighters. Powerful Characters that have access to high-tech attacks or simple magic.
Tier 4: This is where basic humans rarely tread. At this level, magic and high tech stuff is common
Tier 5: Characters at this level are capable of causing high damage to their surroundings.
Tier 6: Fights between players of this level may damage or destroy most unfortified buildings
Tier 7: Battles between characters may result in a destroyed city or two.
Tier 8: Long-term damage to the planet that is fought upon is not beyond possibility.
Tier 9: Goku, Superman, Galactus, Doomsday, Hulk, Etc.