From Tekkenpedia

Demon Scissors
Command	u/f+4~3 4~3 (alternative since T2) WS+4~3 (alternative since T2)
Stance	KND
Damage	25 25,25 (Kazuya in T5 onwards)
Hit Range	M mM (Kazuya in T5 onwards)
Properties	KND
Move Frames		Hit Advantage
25 (TTT) 31 (T5)		KD
Block Advantage		CH Advantage
		KD

Demon Scissors is a move that has existed since the first game of the Tekken series and can be performed by all practitioners of Mishima Style Karate as well as Ogre and True Ogre. During the animation of this move the character will do a forward somersault, hit the opponent with one leg or, in case of Kazuya in post Tekken 4 games, both legs, and land on their back. In both cases, each leg that connects does 25 damage, however, if Kazuya connects with the first leg, the damage of second will reduced to 80% (17 damage) because the opponent will be falling. On a grounded opponent, the damage is 25, even with Kazuya.

[edit] Trivia

• In Tekken 3 and Tekken Tag Tournament, Heihachi would take 5 damage if he whiffed with Demon Scissors. In later games, this was changed so that the player would have to press d when Heihachi hits the ground or simply hold D during the animation, e.g. 4~3,D in order to take damage on whiff. There is however no advantage in doing this whatsoever, as the move retains all the properties of its non-self-damaging counterpart.
• Ogre and True Ogre cannot perform Demon Scissors using the original u/f+4~3 command, but must use one of the two alternative commands introduced in Tekken 2.