Arceus, the strongest pokemon in the world... how do you catch it? Every time you enter the tower of legends, feel free to roll the new arceus dice. If the number is 10, CONGRADULATIONS!
Arceus will appear.
If not, sorry. To make it easier, ever time you beat a member of the elite four (including the champ) you will get the azure flute. This will add 2 to the arceus dice. This means you only need an 8 or above.
There is only one arceus per forum, so if someone has already caught it, you will need to wait till it is released or you need to trade for it.
Arceus has these moves:
Judgement
Perish song
Hyper Beam
Recover
Good luck! Remember, Arceus counts as one of your two legendaries.