In addition to the insanely precise inputs necessary and brutal link timing, this hugely flashy combo relies on a glitch in the way Street Fighter 4 handles stuns. Here’s an explanation by biffotasty himself:
Uses a stun system quirk to force crouching post-stun.
A while back, I thought maybe it’d be possible to break the SFIV combo counter. Somehow get enough hits so that the game loses track and the counter resets or, like Darkstalkers, display weird characters instead of numbers. Turns out that it’s not possible (you can actually test it quite easily in training mode with infinite meter) but I did start thinking of ways in which you might be able to legitimately perform a never ending combo.
Chun Li’s infinites are a perfect place to start but there’s one major problem. As they only work against crouching characters, after the opponent is stunned (and they reset into standing) you won’t be able to use them and there can only be a finite number of hits in the following combo (meaning that at some point it will end).
In steps the ‘stun glitch’, which is a weird quirk of the SFIV system that allows the opponent to block at a certain point during stun but does not end the combo. In fact all combo factors are still in effect. So, meter build and damage scaling are both at 10% (this even applies to chip damage). If you interrupt the opponent during this block stun the combo will continue. 2 ways of doing this are to hit standing guard with a low attack or crouching guard with a jump-in/overhead. This is exploited to turn standing Abel into crouching Abel. At that point, infinites are viable again and no more stun is inflicted. So you can continue the combo as long as you want. Here, I’ve limited the combo to Abel’s full stamina of 1050 points of damage, so that it could technically be performed outside of training mode for a 100% combo.
In all, it’s 276 hits for 1076 damage.
NOTE. After Abel is stunned, I had to look at my feet to make sure I was pushing down-back on an xbox 360 pad I had on the floor. This combo went wrong a bunch of times at this point. Also, there was no set combo after stun, apart from the section immediately preceding the Ultra (cr.HP xx MP.fb, cr.HP xx HP.fb, cr.LK, cr.LK xx EX.legs). I was just looking out for when the damage got to about 1000 before going into that series and it ended up working out pretty much perfect (the ultra had to connect before 1050 points of damage had been reached otherwise, technically Abel would have been KO’d).