Boosted Smash is like, how you say? A sliding up smash with distance...
in my best description, your using the dash attack animation, but replacing it with an up-smash instead to create the picture shown here...
It's practically a useful technique for surprises or chaining, It works well with other characters such as Wolf, Link, and Wario, Falco. Their are many others, but usually those characters benefit from it.
Note- Falco and Snake are the only know possible characters that can boost smash directly after a dash attack... the others have to use the
Dash -> C-Stick -> Z-up+smash technique which is way more difficult than theirs, but can be done very effectively.