In ESO, Two Reagents with the same effect need to be combined in order to craft a potion. Be aware that when crafting potions, some combinations will provide a not always beneficial side effect. The Snakeblood passive will reduce (or with 3 points even eliminate) the negative side-effects, but it’s better to simply avoid them if possible. All effects in poisons are negative, so there’s no need to worry about unintended side-effects with poisons, though poisons with multiple effects will have the duration of all effects reduced. Remember that you have to also provide a solvent, which influences the strength, but not the effect, of a potion. As of Update 18, there are 151 two-reagent combinations.