weakness Potion

To make a weakness Potion (1:30), you put a fermented spidereye in the top slot and a normal water bottle in one of the bottom slots 

For a longer lasting effect (4:00), put a piece of redstone in the top slot and the weakness potion 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