Music of the Spheres Spell and Undead

[drsparnum]

Player bard casts Music of the Spheres, which, among other things, grants fast healing 5 to everyone within 20 feet of the bard. An enemy undead is within 20 feet of the bard. Does the fast heal 5 help, hurt, or do nothing to the undead?

Link to spell:
https://www.aonprd.com/SpellDisplay.aspx?ItemName=Music%20of%20the%20Sphere s

[Mysterious Stranger]

Positive energy only harms undead when it specifically states it does. A good example of this is channeling positive energy. Undead are only harmed by channeling positive energy when it is specifically done to harm them. If a character channels positive energy to heal the living undead are not harmed. Spells dealing with positive energy usually explicitly state that when they target undead it harms them.

That being said Music of the Spheres does not specify it harms undead, or even that it is actually using positive energy. It does however specify that” all creatures within 20 feet of you, friend and foe alike”. Undead are creature and if they are within 20 feet of you, they gain all the abilities stated abilities of the spell. Since positive energy is an energy type, they even gain resist positive energy 10.

[Diego Rossi]

Undead can benefit from fast healing. It isn't a positive energy effect, it is "just like natural healing" Universal monster rules, fast healing. Several undead have it or can get it in specific situations.