A player in my new 5th Edition campaign wants to play a cleric of Mask. He was curious why Dispel Magic is listed on the domain spell list, and I have to admit that I am equally confused. The spell is already an option available to clerics.
Is this an errata of some kind? Is Dispel Magic on the Trickery Domain list meant to be a different spell? Invisibility is the usual 2nd level wizard spell that cleric domains of this type would get.
I attempted to look for an official errata page, but didn't have any success, so hopefully someone here will know! 
Domain spells are often from the cleric spell list already. Take a look at Life clerics, for example! So, there's no error here.
Recall that the domain spells are not meant as such to augment the list of spells available on the list, although some do. What they do is allow that spell always to be prepared without counting against the number of spells the cleric prepares. What it guarantees, basically, is that the cleric can always have thematically appropriate spells available to him without compromising other choices the player might make in spell preparation.
Because a classic Loki trick is to remove other peoples' magical disguises at the worst possible moment 