The easiest way I know is using distance as an instance variable on your character sprite. Something along the line of:
Every tick
Pick the tile by compare, tile.ID = whatever number it is
Action
set variable, distance(sprite.x,sprite.y,tile.x,tile.y)
Then use that variable to do what you want.
If the tile needs to change over time, you could use a variable for the tile ID, etc.