U need the same. So 2 max 2s. N it will only make a 3 star. And 2 3 stars make a 4 star

U have to have 2 of the same , at same level. Like for example, gorev the moltive 1, u wld have to hav 2 of him. Two 1 star characters will be paired to make a 2 star one. And then to promote 2 star one, u wld need the exact same one with 2 stars to promote .