Cool concept! Nice gameplay idea to put rocks so the player can switch position... My best score is 3500
EDIT: I played on my mobile where you don't have the clue "hovering" a tile. The blue mark on PC make things easier.
The issue for me was that it is hard to guess where you'll end up. Maybe too hard to implement for a game jam but a visual representation of your Z and where you'll really end up would make the management easier (but maybe too easy some time)