Like I said in part 1, the Horn can be used to weaken hordes/armies up until the Last Battle. Once the battle starts though, the Horn can no longer be blown. But the Last Battle is when it's SUPPOSED to be blown, right? We'll it will be. The Horn is blown every hour automatically and the Heroes of the Horn will fight for whichever side holds the Horn!
When the Last Battle starts, the side of the player holding the Horn earns a bonus 800 points. Then every hour during the Last Battle, whichever side holds the Horn will earn 100 points towards their side. Doesn't matter if the player holds it for the whole hour or just the last 2 seconds. All that matters is who has it when the hour changes. When the Last Battle ends, the side holding the Horn earns a bonus 2,500 points.
So if you add that all up (800 + 167*100 + 2500), that's 20,000 points that can be earned by holding the Horn. There is a chance that the Horn may not be held by anyone at an hour change (due to it being used before the Last Battle starts). If that happen, neither side gets those point.
After the Last Battle is over, the Horn will vanish from whoever has it so it can be found again when it's needed for the next Age.