Advanced Footsies/Fundamentals
This is the X-factor. This is how the best players win even though they don't have optimal damage. Transcends all 2D fighting game mechanics. Work with someone who mastered these skills within the limits of SF2, with no dashes, no parries, no fireball invincibility and proximity guard that activates from full screen. These tools are that much more effective when you have access to modern game mechanics.