Scripts

Let me point out the exact error right away. When you assign the return value of the GetObjectPosition function to crearure_positions[k], the corresponding element becomes a number instead of a table of three elements. Therefore, you need to do this again: creature_positions[k][1], creature_positions[k][2], creature_positions[k][3] = GetObjectPosition(monster).
And in the IsTilePassable check, you first need to save the corresponding elements of the table in local x, y, and z, and then pass them to IsTilePassable.
And it is precisely because of this that the error "attempt to index a number" occurs. After all, creature[k] is just a number.