Guard Break and Focus Attack
Street Fighter EX, the SF franchise’s first foray into 3D, wasn’t nearly as well received as Street Fighter IV (allegedly- personally, I’ve never met a Street Fighter fan that didn’t adore the EX series). Even so, some of Street Fighter IV’s concepts have roots in the EX series. The most obvious example of this is the Guard Break.
In EX, by pressing two buttons of the same strength (any two, it didn’t just have to be strong+forward), the player could spend one bar of meter to execute a slow but unblockable attack that would leave the opponent stunned and open to any number of devastating combos.
EX2 added the ability to Cancel Break, allowing the player to cancel any blocked attack with an instant Guard Break, improving the move’s utility considerably.
For IV, the Guard Break became the Focus Attack and the Cancel Break became the EX Cancel. The move and it’s mechanics lay the groundwork for SFIV’s metagame, perhaps proving that the EX series had more untapped potential than anyone was able to recognize at the time.