Normally you can only melee Figures (Figures are Creatures or Buildings) if you could move into their space if they weren't there. This means land Creatures can't attack things in the water or things far away. The exception is when a Figure melees you. If one Figure melees another then the other Figure is able to attack him back regardless of where the first figure attacked from. Battling Back is like a normal melee attack in that you must be undimmed to do it and you become dimmed after you Battle Back. So even with Battle Back a Figure can still only make one attack per round.
For example this Ulg Turtle in the ocean just attacked your Red Imp standing on the land, the Red Imp now has the option of attacking the turtle back.