The King of Fighters XIII - Kyo and Shen combos
Combos that have Hyper Drive Activation mid combo AND Max Cancels as well are amongst the hardest to execute in the game.
Doing a Hyper Drive Activation mid combo is tricky. If you cancel an attack with hyper drive activation during its active frames you will dash forward during activation. However, if you delay the activation after an attack in its recovery frames, a s.HP will come out immediately after the activation. This delayed activation can cause combos to drop, particularly if the combo afterwards doesn’t start with HP; OR if it does, another s.HP might accidentally be input by the player thinking the s.HP was an active frame cancellation.
Not only are these types of combos difficult, Kyo's ones can be considered to be one of the hardest in the game from an executional standpoint. Shen's ones, albeit a little easier, are still very difficult to pull off, particularly because the Tenren Ken (Turning Chain Fist) followed by Gekiken (Raging Fist) can come out as his super Tatsu! Gekiken if done too quickly.
Have a look at the Kyo's and Shen's combos, performed on a KeyCade KKL by BoAngel: