I'm curious about this little note under the main melody on J Core music

[primal raptor]

What's it called? And how i can make it ?

https://youtu.be/v4NEn3bhoCw?si=wGH4ZXDn-x7JYCFN
Link for the source i found

I don't seem to understand it because the video is quite fast

I love the fast phase songs especially this one

[vale ginkgo]

Some composers make the note shorter (typically halved) and add a note an octave under it usually that sounds well and repeats a few times, this is used when you want to make your melody appear faster and its very wide spread in gothic hardcore/jcore, idk the name though

[tall seal]

adding to what Yorxe said:
it can be any notes in the scale that you're in it

but commonly it's the dominant of the scale or previous note

[vale ginkgo]

i do an off scale note sometimes

thats a half step higher than the previous note

and it works

[summer vortex]

I mean, it just seams like you take the chord in the harmony, use the root note, and add that to the melody as full notes or ornaments to other notes. I guess it sounds good because that note runs with the harmony and creates a ground for which to return to during melodic lines.

If you want an actual name tho for the short notes that create a quick step up, it should be some sort of classical ornamentation. As for the actual production technique I have no clue