Instructions
Level up your character to the mid-30s to low 40s by completing all the quests in the game and defeating enemies.
Allocate your skill points (SP) in the following manner to create a "Whirlwind Barbarian," arguably the strongest barbarian class type: Combat Skills - 1 SP to Bash, 1 SP to Leap, 1 SP to Stun, 1 SP to Leap Attack, 1 SP to Concentrate and 20 SP to Whirlwind; War Cries - 1 SP to Howl, 20 SP to Shout, 20 SP to Battle Orders and 1 SP to Battle Command; Combat Mastery - max out the Axe combat mastery and distribute all bonus skill points between Iron Skin and Natural Resistance.
Equip your character with the most powerful axe that you have found in the game thus far, and always keep a look out for a new more powerful axe.
Enter the Sanctuary in the bottom level of Hell and defeat all the monsters. Activate four of the five glyphs that summon Diablo by clicking on them.
Open a town portal by pressing the "I" button on your keyboard and right-clicking on the blue "Town Portal Tomb." Click on the portal to return to town.
Click on your chest and stash all unnecessary items there to clear space in your personal inventory. Click on a merchant and purchase as many "Greater Healing Potions" as possible, filling all inventory and belt slots.
Click on the town portal to return to the Sanctuary. Click on the remain glyph to summon Diablo.
Attack Diablo with your Whirlwind skill while he's on the move by clicking on him. Run around him in a small circle when he stops and raises his arms, indicating he's about to attack.
Heal your Barbarian when his health gets low by pressing number keys 1 through 6 on your keyboard. Run away to safety, open your inventory by pressing "I" and transfer additional Greater Healing Potions to your belt before resuming your attack.
Return to town and purchase more healing potions if you run out. Return to the Sanctuary when ready and resume the onslaught. Keep your character alive and continue fighting until Diablo dies.