So with the major additions being the Maximoffs and Ultron, we have more more more than enough issues to countdown with 637 days remaining. I'll start with the Maximoffs, go into their individual history, then move onto issues and stories featuring Ultron.
Okay, let's do this. B.A.U. = Before Age of Ultron
And we start with Scarlet Witch and Quicksilver fist joining the Avengers! I would have covered their first appearance in general but it seemed wrong to start off an Avengers countdown with an X-Men issue. Will start from the beginning from tomorrow onward.