There are a couple things you might be running into. One is that JJ2 is of course always changing the player's xSpeed on its own, so if you make a single short-term change, in response to something like one of the onFunction# hooks, then that change is not going to last very long before JJ2's normal speed handling takes over. But onPlayer works constantly instead of as a one-time thing, so naturally it's going to have more visible impact. The other is that p is deprecated and may not (should not) work in all situations, and you should use the actual jjPLAYER@ argument available to onObjectHit and onFunction# instead.