How do I make a potion to kill a bunch of mobs at once. A splash potion i believe. Water, nether wart, spider eye, fermented spider eye, gun powder?
For zombies, skeletons and a few others (undead mobs) I think that it's an instant health splash potion. For blazes and most others, instant harming splash potion. That's the correct recipe for those - I think!
Depends what your killing. Undead things you kill with instant health. Spiders and creepers are killed with potions of damage.