Exactly as the name says, how does the morningstar work against say a skeleton which has DR 5/bludgeoning, since a morningstar is both bludgeoning AND piercing? I have looked online, and found some that say the DR applies because part is piercing, but I have also found some that say because the skeleton does not have DR against BOTH bludgeoning AND piercing, the DR doesn't apply. Really need to get this clarified, as I am about to literally take on endless waves of the undead.
The morningstar will bypass their damage reduction.
From the PFSRD on Weapon Qualities (emphasis mine):
Type: Weapons are classified according to the type of damage they deal: B for bludgeoning, P for piercing, or S for slashing. Some monsters may be resistant or immune to attacks from certain types of weapons. Some weapons deal damage of multiple types. If a weapon causes two types of damage, the type it deals is not half one type and half another; all damage caused is of both types. Therefore, a creature would have to be immune to both types of damage to ignore any of the damage caused by such a weapon.
The morningstar deals both bludgeoning and piercing damage, and so bypasses DR/bludgeoning.