Dezuray, I think the Ice/Fire type is a great idea! Here's a stupid idea, what about a Ice/Fire unicorn Pokemon. We really haven't made a unicorn Pokemon.
We DO have a Ghost type legendary Pokemon but we could make another. There is this Japanese mythical cat called a Bakineko and it's a ghost. Maybe that could be the cute legendary Pokemon like Mew, Celebi, Jirachi, Manaphy, and Shaymin. But the thing is we already have a cute cat legendary so it might not be the best choice. It could be a Ghost/Normal type.
A Gryphen (or however you spell it) would make a great legendary Pokemon. It could probabley be a pure Flying type Pokemon.
Now let's think about the Poison type. We have already made a snake, spider, frog, pufferfish, and jellyfish Pokemon that is at least PART Poison type. What about a Gila Monster. They're poisonous. It could probabley be a Poison/Ground type.