I saw that it said
However, Shadow Force provides a good deal more power, so much so that Lugia and Giratina risk being OHKOed by Shadow Force after taking Stealth Rock damage provided Arceus has used Swords Dance once, is Adamant, and is holding Life Orb.
Shadow Force also alleviates any fears about Wobbuffet. Unfortunately, Shadow Force's charge turn makes it easy for the opponent to play around.
But I didnt see that arceus could learn Shadow Force. what's going on?