The jab grab is a character-specific technique performable by Pikachu, Mario, Ness, and Luigi in Smash 64. It is performed by jabbing, and then using a grab instantly afterwards. Additionally, performing the grab too late will just perform another jab instead. It is a simple form of shield pressure. Jab Grab will only work if it is connecting with another object. It will work on a hurtbox, a shield, and even the Piranha Plants on Mushroom Kingdom.
Level 8-9 computer opponents occasionally use this technique as well, more often with Mario.
This technique is highly useful in competitive play, and it is one of the key reasons why certain characters are considered better at pressuring, as not having this technique highly limits shield pressure.