Well, I tried both Arctic Octopus and Ulitharid in my Rainbow deck, and Ulitharid seems to work a lot better. I think the main reason why this is is because Arctic Octopus stops nasty creatures for a temporary time and a large cost. Ulitharid stops nasty abilities forever and it costs very little, even with all the other Aether items in a Rainbow deck. Sure the Octopus is useful, but once 4+ creatures appear, you're not going to freeze all of them. Its quanta consumption is also a problem. The Ulitharid is nimble, not very costly, has a decent attack, and a great ability that can destroy decks easily.