I don’t have a lot of experience using Region3 myself, but from things I’ve read you’d make a region based on a part’s size, you could then use WorldRoot to detect what is inside that region every frame. I believe I’ve read that Region3 also has some sort of on enter trigger? Though I’d assume it’s like Touched
I’d advise against Region3 every frame. More performant options include:
Magnitude check to a couple key parts in each thing you can damage (head, hrp in a character for example), or positional check within the bounds of the hitbox
Raycasting with a distance the length of the hitbox whitelisting or using collision groups to only check for things you can damage
GetTouchingParts each frame to find parts that are currently touching the hitbox.
I can’t watch your video as it’s in Windows format and I’m on mobile currently, so your preference may depend on the tool. My preference would likely be Raycasting as a good setup with CollisionGroups could be the most performant of all the options, and potentially gives the option for more directional tools and weapons too.