I’m going with 4 difficulty levels! Going with a bit of a Game Dev Theme (fantasy rpg flavor).
Easy (Brother’s Laptop)
Mana
Blade
Fish
Spell
Arrow
Medium (Dad’s PC)
Quest
Dagger
Potion
Magic
Sword
Hard (Indie Startup’s Servers)
Shield
Prayer
Bulwark
Polearm
Wyvern
Expert (Game Studio’s Mainframe)
Elemental
Gravestone
Nightmare
Subterfuge
Incarnation