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Depends on the set, Palkia with mixed sets is fairly common and thus Timid is not recommended for those. But Timid is the go to nature for it when going all special.
Why Naive over Hasty? Because it's an offensive Pokemon so you may as well put the defence you have over to one side and let it be semi competent at it instead of having two meh defences so people don't lower the slightly higher Sp Def