Mitja said:Whether Blissey changes type is key here from a competitive standpoint (and without knowing what gen 6 will add), all the other guessed changes won't make much of a difference.
Fairy being weak to Poison is a really poor buff and wont really affect usage of its moves unless something hard to take down becomes weak to it.
Blissey being weak to Poison and Steel while laughing at Dragons? That's it. No more "just throw a physical fighting move at it", you will want either a Poison or Steel move on an offensive pokemon in your team. I love the thought!
Steel-types nullify Poison, so although, it may sound like a poor buff. This is rather a strong buff.