You can unlock it in Royal Arena (Arena 7)
Single target medium range troop with high hitpoints.
Like Giant he prefer attack buildings.
His gun and long range attacks makes him a more flexible option than the Giant is.
You can comb him with Princess with also long range and she can be shielded by the Royal Giant.
To counter him you can use Minion Horde or Skeleton Army.
When you placing him on the end of the bridge he immediately attack the Arena Tower.
You can use him as a tank.