Do effects stack?
I got this from wowhead site paladin class overview section.
Auras
You can only have one aura active at a time. You’ll have to decide what is best for the situation. Other players can also let you know what is best to use. If there are multiple Paladins in the same group, they can each have a different aura active, but multiple Paladins cannot stack the effects of the same aura. If you find yourself in a party with another Paladin, ask him or her what aura he or she is going to use, then use a different one that will complement it.
Multiple Paladins will still all use Devo Aura because of Aura Mastery. Our AM is used as a raid cooldown for hard hitting AOE boss mechanics.
Holy Paladin Auras have been terrible last few expansions and need an overhaul. None of the mitigation for Devo is even counted on healing logs. In Legion you had no choice but to bubble when using AM/Sac. And Mercy is just lol.
Note that multiple stacks of Devo can still be useful for coverage, for example on a fight like Sivara where the two pallies will be on opposite sides ~50% of the time and everyone is moving around a lot.
But yeah, if it’s a tight stack and you don’t need the AM + Devo combo to counter a big burst, you could make a case for one pally running Mercy. It’s not amazing, but hey, it’s a few thousand HPS (and the lucky pally will look great on WCL ranks).
If you have three pallies, you can have each aura active. However, multiples of the same aura, do not stack. I have seen some successful 2 pally with any other aoe healer, do very well.
Devo for big raid wide with aura mastery.
Mercy for constant small Regen. Activate aura mastery with mercy and increase the aoe healers output. So you kinda support your buddies heals with it, not your own so much but still works (Unless they changed the wording it says "increases the amount of healing done by aura mastery by 100 percent and increases the amount of healing received by targets affected by Mercy) . Working that in with tranq, or just aoe effects, gives a nice boost to the aoe heals. Keeping a raid up that way.
There are, fun, combinations, that aren’t optimal but are perfectly viable for casual raiding
Very cool. I love all these utility skills