Potion of Poison

To make a Potion of Poison (1hp/2.5s;0:45), you first need to make an awkward potion

after the awkward potion is finished put a spidereye in the top slot and wait for the Potion of Poison to finish

For the Poison II effect (1hp/1.2s;0:21), put a piece of glowstone in the top slot and the Potion of Poison (0:45) in the bottom slot

For a longer lasting effect (1hp/2.5s;1:30), put a piece of redstone in the top slot and the Potion of Poison (0:45) in the bottom slot

If you want to make a splash Potion out of it you simply put a piece of gunpowder in the top slot

And if the splash potion is not enough for you and you want to make a lingering potion from it, then you just put a bottle of dragon´s breath in the top slot and the splash potion in the bottom slot