The concept of ‘priority’ is mentioned in a few of the character spotlight videos, but isn’t really explained anywhere else. So what is it and how does it work? Is there any way to know whether a move is high or low priority?
In all situations except when invulnerable, characters have vulnerable hitboxes. When they attack, they can also have attacking hitboxes.
The basic rule is that you get to hit the opponent when one of your attacking hitboxes intersects one of the opponent’s vulnerable hitboxes.
When we speak of a move having “high priority”, it’s just shorthand for saying that the move has attacking hitboxes that are far ahead of its vulnerable hitboxes, such that it’s more likely to hit the opponent before the opponent hits you.
What Thelo said is correct. Here’s an example of what he’s talking about. This is jigglypuff’s back air in Melee. It has ridiculous priority because the red hitbox that hits other people extends way beyond the yellow hurtbox where she can get hit.
Incidentally, does anyone have hitbox data on fantasy strike?