I'm in love with this design. You've packed so much into such little space while keeping the rules and operations crystal clear. Amazing work!
In fact orthogonally is a very common instruction in board games, that means you can move only in 90º (left, right, up or down), so I used this word due to layout limitation, to say you can't move diagonally.
Rules say "Move one tile orthogonally", so you just move, from START, right or down one tile, then follow the rest of the rules, then move again orthogonally (left, right, up or down).
Also in the rules it says "Reach the BOSS", so you know you must get in that direction.
It is just that, one tile at a time orthogonally, but not diagonally.
Hope it helped.