Craft a Brewing Stand
Gather Blaze Powder for fuel
Gather Water Bottles
Brew an Awkward Potion using Nether Wart and Water Bottles
Add a Fermented Spider Eye to the Awkward Potion to make a Potion of Harming
Add Glowstone Dust to upgrade it to Potion of Harming II
Add Gunpowder to make it a Splash Potion of Harming
Add Dragon’s Breath to make it a Lingering Potion of Harming