So Ner'zhul in a single act, creates 100's or portals that rip apart a world, doesn't count.
Azshara's highbourne, create a small portal that is maintained for weeks and months and has it's maintainers replaced constantly, who also get the aid of demons to strengthen it and funnel energy from the Well of Eternity and then later have an old god's artifact(The demonsoul) strengthen it even further, only so an avatar of Sargeras can come through... counts as a single act?
Yeah no, Ner'zhul takes this one.