Monsters that walked the planes. Which has never happened before.

[Things like Elder Gods, Outer Beings, tentacled horrors from beyond time were the only things that could do that, as far as she was aware, and that was what the Eldrazi were. Or may as well be.]

I was there for a couple of weeks both times. My friends and I, the second time, made an oath and formed the Gatewatch. It's...basically just a group of us Planeswalkers that go from world to world dealing with monsters or threats that can travel like us.