Aggro deck from a beta player - actually works. Not a perfect list, there are still many cards I don't have.
Originally I was running 3, then 4 one-cost heroes. But they are so useful. Sentinel helps keep your hand full, and lets you play a mix of smaller cards on turns 3, 5, and 6. Wolfsbane and Kazar are very efficient, 3c 7p and 4c 9+ power are very common, consistent reliable payoffs. I think you could play only 5 one-drops but 6 doesn't feel like too many in most games, as long as you get some card draw from Sentinel and Mantis.
Armor is not crucial, but he is good for this deck. I picked him from my small collection because he is protecting my drops from very popular Elektra, and helps shut down locations like Danger Room, Knowhere, or the 'destroy everything at end of turn 4' locations. Because you fill up so many slots, you can't afford to play a 2-location game. Also blocks Killmonger. Could be replaced by Colossus.
Mr Fantastic is more or less a preference vs. Iron Heart - I find her 0-power to be frustrating, taking up a slot but not contributing. But those games where you play three 1-drops on the first two turns then drop Iron Heart on 3 for a perfect +6 buff feels better than Mr Fantastic usually.