I may go back and listen to other trailers, to see what the super effective sound is. I think it is safe to say that Oorotto is definitely not rock. Which I like. Unless it was normal effective and he is Grass/Rock or Bug/Rock. He could even be part Fiary like some hoped for. (I don't think he would be part bug though) He might have even a surprising type combo like Malamar did.
Let me listen to the attack again and I will say, it is hard to tell at the moment.
Listening to to the attack sounds again, it sounds like the fire attack was super effective against Oorotto. Therefore making it part grass or bug. I don't think it is Grass/Bug for sure or a level 50 should have 1 hit all those lv 25s. So Orotto is not part fire, water, rock and dragon. (I could still be wrong, the sound with Oorotto is not that clear, but it sounded like super effective.)
So there are a good amount of choices to go on still, but at least that cancels out rock type.