Navigate a grid by keyboard

As I've learned accessibility in Storyline, where the Tab key highlights next is determined by the Focus Order. That will also always be a sequential order, in that users can press Tab to advance down the list of Focusable objects as well as Shift-Tab to go back up. If by accessibility you mean users could navigate an on-screen indicator around a grid using WASD or the arrow keys, that's going to require a custom solution of triggers and/or JavaScript.

The ways in which I see solving that actually overlap greatly with the first part of your post. When you say the slide starts at the beginning, what happens in that beginning? I've imagined a grid so far, and you mention battleship, but is there a movie that plays or is the player's location just resetting?