In every Pokemon franchise, catching the legendaries mean you have succeeded over the game. Here are the tips and tricks for the "Pokemon Sun and Moon" to catch Marshadow and the rest of legendary Pokemons.
Normally, legendary Pokemons are hard to catch, but having them in party gives a particular boost and pride to the Trainer. For Pokemon Sun and Moon, there is one box legendary who goes by the name Tapus.
However, the Alola region has a lot more of Legendary Pokemon. For example, Solgaleo and Lunala are both box legendaries that can be obtained depending on which game you play (Sun or Moon). All you need to do is to progress through the story. There will be a part in which they will challenge you to a battle and they will be ready for catch.
Then there is Cosmog. He is actually a pre-evolution of Solgaleo or Lunala. To have Cosmog, you have to complete the game and become the Champion first. After which you have to go to the Altar of Sunne. Then you must go through the portal. In Pokemon Sun, the portal is open at night, while it is open in day for Pokemon Moon.
As you go to the Lake of Moon, go to the top of platform where you will get to face Cosmog. He can evolve into either Solgaleo or Lunala depending on your version.
Then there is Marshadow, a mysterious legendary in Pokemon Sun and Moon which surfaced after data mining and trademark leaks. Sadly, Marshadow is not for catching. But you can still have him via Mystery Gift distribution.
Pokemon Sun and Moon has revived interest in the Pokemon franchise. Recently, "Pokemon Go" made waves as it became available both in iOS and Android by Niantic.