This is a pretty common tactic in any other fighting game. It's called an empty jump in.





It's most effective only if you know your opponent is going to block (and not anti-air or attempt to beat it out). The idea is, if you're jumping in for a high mixup and you know your opponent is going to attempt to block it, you can use that to simply not attack and sneak in a low or a grab.



It works because most people block on a sort of rhythm, they anticipate the blockstun/blockpush and react afterwards. In the split second this takes, while they're waiting for that block confirm, you can easily just sneak in a different attack (usually a quick low, since they're going to be blocking high since it's a jump-in) but Grab in this situation works equally as well for the same reasons. But if they're mashing out, or attempting to anti-air, you're most definitely going to be hit.



This works great in smash bros because shields are so good to begin with, and almost every aerial is unsafe on block. The most powerful effect of this is how well it breaks the rhythm of the opponent.



But if you're predictible with it, you're likely to be killed by an upsmash.