Brew an Awkward Potion by placing a Water Bottle in a Brewing Stand with Nether Wart
Add a Glistering Melon to the Awkward Potion to make a Potion of Healing
Add Fermented Spider Eye to the Potion of Healing to turn it into a Potion of Harming
Optional: Add Glowstone Dust to make it a stronger Harming potion
Optional: Add Gunpowder to make it a Splash Potion of Harming
Optional: Add Dragon’s Breath to a Splash Potion of Harming to make a Lingering Potion of Harming