It can't be caught, and in the first phase, it is invincible. You'd have to let it wail on you for a couple of turns, until plot comes in and breaks the barrier. (Wouldn't be able to put this in anyway)
At that point, you fight a pokemon with stats if that pokemon were Lv. 150 or 200. Its stats are either equal or above Arceus' 120s, with the exception of HP, Def and SpD. Which is strong.
By this point, you should have pokemon which CAN fight it, but since it is a plot fight, and not a real fight, I can make it as long as I want, tbh.