Brew Awkward Potion: Water Bottle + Nether Wart
Add Spider Eye to the Awkward Potion to make a Potion of Poison
Optional: Add Redstone Dust to extend the duration
Optional: Add Glowstone Dust to increase the potency
Optional: Add Gunpowder to make it a Splash Potion of Poison
Optional: Add Dragon’s Breath to make it a Lingering Potion of Poison