Marvel vs Capcom 2/The Engine
Unblockables and Bugs
(These will be their own sections)
Unblockables: Sentinel's Fierce mouth beam, Doom's crouching HK, and Cable's fourth bullet. Unblockables are not blockable if they collide with your hitbox. These are discrete from cross-ups - there are many cases in Marvel where characters face opposite to their screen positions (for example, Magneto air dashing over a character will not have where he is facing reset until he lands) which thus create very hard to block cross-ups.
There are DHC unblockables that work when you are using a character whose super flash doesn't cause the other person to block. After the initial superflash you must DHC very quickly into someone like Iron-Man or Morrigan. Iron-Man's Proton Cannon is instant when you DHC into it so if the person wasn't block they're going to get hit and since there wasn't anything to block in the first place it's unblockable.