Brew an Awkward Potion using a Water Bottle and Nether Wart
Add a Fermented Spider Eye to the Awkward Potion to make a Potion of Poison
Add a Fermented Spider Eye to the Potion of Poison to make a Potion of Harming
To make a Splash Potion of Harming, add Gunpowder to the Potion of Harming
To make a Lingering Potion of Harming, add Dragon’s Breath to the Splash Potion of Harming
To make a stronger Potion of Harming, use Glowstone Dust on the Potion of Harming
To extend the duration of a Harming potion effect, use Redstone on the base potion before converting it