This effect is really easy in theory. You have to create a new frame in weapon.dat which have the "opoint" for the attack in it. This frame is only activated in a certain character. You just have to care about two things - the "wait" in the frame where you activate the new weapon frame with "weaponact" must be zero. If not, more attacks will appear, one after another. The other thing is that you have to create a new frame in all other weapons with type: 1 (excluding the arrows and the ninja star) which the character can use.
In the study example, I set the "weaponact" in frame 22 and 27 to 100. Both frames have an "attacking" of 1. Normally, the itr of entry 1 is activated. But other weapons needs such a frame, too - if there shouldn't be a weapon if the hand of the character while he's attacking. But that's not really hard. Just copy the frame which was noted in "weaponact" earlier and change the number to 100. In the weapon with the special attack, you have to note the "opoint", too.
Here's the study example:
SpecialAttack Weapon |
Inspired by MH-Razen