I wanted to pick your DM brains about allowing a Cleric of the Tempest domain to swap one of their domain spells.
One of the players in our campaign would like to swap Control Water (PHB, p.227) for Storm Sphere (XGtE, p.166). It seems to be in line with the whole flavour of a Tempest Cleric and they are both 4th-level spells.
Note: Storm Sphere appears in Xanathar's Guide to Everything, so it had not been published at the time when the Tempest domain was published.
Would it be unbalanced to allow this spell swap for the Tempest cleric’s domain spells?
I would really appreciate any answers that draw on own experience of allowing tweaks for a Cleric domain spells.
Best Answer
As a DM I would call it slightly imbalanced
Since domain spells are considered always prepared, there is a quick trick to figure out value/balance; reverse the conditions.
At 7th level, a Tempest cleric gets two domain spells; Control Water and Ice Storm. These are always prepared above and beyond what the cleric can have prepared. For the sake of argument, we'll say that they can prepare 11 non-domain spells (level 7 + 4 for an 18 Wisdom)
This means that if they want to also have Storm Sphere they would have to use up one of their prepared spots. But this brings up another issue I'll address at the end (Hint, they can't do it).
If we reversed the spells, Control Water must be manually prepared and Storm Sphere is a "freebie", what is the likelihood that the cleric would choose Control Water as one of those 11?
Unless you were specifically going on an adventure where there is a great chance to encounter a large body of water, I would imagine the chance being very low. Whereas Storm Sphere can be a useful attack no matter what.
So you would be trading a niche spell, Control Water, for an always useful attack spell, Storm Sphere. To me, it sounds like the player is just looking to not be stuck with a rarely used "freebie". They should feel sorry for Arcana clerics that are stuck with Nystul's magic aura and Leomund's secret chest...
Now, is it going to change the world? No
Will it give the player any great advantage? Unless you're going through a water campaign, it's basically an extra spell they can prepare.
The second issue is that Storm Sphere is not even on the Cleric's spell list. It would be impossible for a cleric to prepare this spell under normal means. So not only would they essentially be getting an extra preparation slot, but they would be getting a spell that no other Cleric could cast.
Is that game breaking? Still no. Lot's of clerics have domain spells that no other cleric can cast. Once again, Arcana clerics get Nystul's magic aura and Leomund's secret chest. But it does give them another edge up that may make other clerics wish to switch out their Domain spells to something cooler/more useful.