Shapechange: Spell Save DC and Spell Attack Bonus

The Spell:

Shapechange: 

You shape-shift into another creature for the duration or until you take a Magic action to shape-shift into a different eligible form. The new form must be of a creature that has a Challenge Rating no higher than your level or Challenge Rating. You must have seen the sort of creature before, and it can’t be a Construct or an Undead.

When you cast the spell, you gain a number of Temporary Hit Points equal to the Hit Points of the first form into which you shape-shift. These Temporary Hit Points vanish if any remain when the spell ends.

Your game statistics are replaced by the stat block of the chosen form, but you retain your creature type; alignment; personality; Intelligence, Wisdom, and Charisma scores; Hit Points; Hit Point Dice; proficiencies; and ability to communicate. If you have the Spellcasting feature, you retain it too.

Upon shape-shifting, you determine whether your equipment drops to the ground or changes in size and shape to fit the new form while you’re in it.

The Question: If my level 17 Druid with 10 Int and 10 Cha uses Shapechange to turn into an Adult Gold Dragon, retaining these scores, what would be the spell attack bonus and spell save DC?

The statblock reads: 

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 21, +13 to hit with spell attacks)

My understanding would be that my Druid casts Guiding Bolt and Zone of Truth from the Dragon's Spellcasting feature not with +13 and DC 21, but with +6 to hit and DC 14 based on having a +0 modifier and a +6 Proficiency Bonus. Is this correct?

Added wrinkle: My druid has an amulet that grants +2 Spell Attacks and Spell Save DC. If I choose that it changes in size and shape to fit the new form, its bonuses should still apply and lead to +8 and DC 16 accordingly, yes?

Please note that this is just the way I rule it, but I know other people do it differently. See, for example, page 2 of Does Shapechange Retain Your Spellcasting or the Monster's?

And well, from the same thread, this is my opinion:

Quote from Tarod_ >>

Quote from R3sistance >>

Quote from Plaguescarred >>

Yeah keeping both Spellcasting would definitly give more options but would also create issues in that you potentially have two spellcasting ability, attack & spell save DC etc...

I would also welcome a Sage Advice Q&A  on this topic.

I don't see that as a major issue, if a Wizard multiclasses into a Cleric, they would have separate spellcasting abilitiy attacks and spell save DCs between the two classes, so using shape change would be no different, the creature's spells would use the creatures spellcasting ability attack & DC while the caster's own class spells would use their spellcasting ability modifier for attack and DC.

 That's also my understanding. You follow the monster's stat block when you use one of its actions, like a melee or ranged attack, or a spell it has.

EDIT: similar to when you wild shape into a Beast, where you use directly the information from the stat block if you use those attacks.

Quote from Disil >>

[...] Added wrinkle: My druid has an amulet that grants +2 Spell Attacks and Spell Save DC. If I choose that it changes in size and shape to fit the new form, its bonuses should still apply and lead to +8 and DC 16 accordingly, yes?

 Regardless of how you rule the first question, I'd say adding the bonuses is right.

You say you follow the monster's statblock, but the statblock changes based on the retention of the mental stats, so the DC and +attack would need to be recalculated with the different stats, yes?

Well, Shapechange doesn't say the stat block needs to be updated based on your mental stats, just you retain them (e.g. for calculating ability checks not printed in the block, or saving throws)

That's why I don't think it's strictly necessary, but I can see a DM ruling it the way you explained.

Interesting, appreciate the perspective. To complicate matters further, we're a group playing online through Foundry and I just tested what happens when I transform into an Adult Black Dragon and it's..weird.

- It retains all my Druid spells with the appropriate +hit and DCs (without any items and reducing proficiency to 5) which is debatable, but certainly could be made a case for.

- It adds all the spells and spell-abilities from the Dragon's statblock under "additional spells" with the following changes:

All actual spells like Vitriolic Sphere or Melf's Acid Arrow use my Druid's spell save DC of 19 and +hit of 11. This is simply wrong, it should be either 17/+9 or 13/+5.

All abilities like Cloud of Insects and the Fear from Frightful Presence (even though it says that you use Spellcasting  to cast Fear) use DC 13 which is just +5 from proficiency and +0 from my 10 Charisma which would be correct if we go with my initial read.

However, for the Adult Gold Dragon, even the Weakening Breath only has a DC 13 which makes no sense at all since it's not using the Spellcasting Feature.

Acid Breath and Rend retain the original DCs and +hit from the stat block. Which is correct.

So yeah..it's a mess. And while possible to manually rewrite abilities in Foundry and I mostly know how to, doing so for all possible creatures and potentially each time is..pain.

Well, recalculating for each creature would be painful :(, I agree, which is one of my reasons for not doing it, or at least not in the middle of a session

Also, I just remembered this thread after your last reply, in case it helps with what's happening in your case: Do "proficiencies" include the Proficiency Bonus?

Quote from Disil >>

The Spell:

Shapechange: 

You shape-shift into another creature for the duration or until you take a Magic action to shape-shift into a different eligible form. The new form must be of a creature that has a Challenge Rating no higher than your level or Challenge Rating. You must have seen the sort of creature before, and it can’t be a Construct or an Undead.

When you cast the spell, you gain a number of Temporary Hit Points equal to the Hit Points of the first form into which you shape-shift. These Temporary Hit Points vanish if any remain when the spell ends.

Your game statistics are replaced by the stat block of the chosen form, but you retain your creature type; alignment; personality; Intelligence, Wisdom, and Charisma scores; Hit Points; Hit Point Dice; proficiencies; and ability to communicate. If you have the Spellcasting feature, you retain it too.

Upon shape-shifting, you determine whether your equipment drops to the ground or changes in size and shape to fit the new form while you’re in it.

 

The Question: If my level 17 Druid with 10 Int and 10 Cha uses Shapechange to turn into an Adult Gold Dragon, retaining these scores, what would be the spell attack bonus and spell save DC?

The statblock reads: 

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 21, +13 to hit with spell attacks)

My understanding would be that my Druid casts Guiding Bolt and Zone of Truth from the Dragon's Spellcasting feature not with +13 and DC 21, but with +6 to hit and DC 14 based on having a +0 modifier and a +6 Proficiency Bonus. Is this correct?

 

Added wrinkle: My druid has an amulet that grants +2 Spell Attacks and Spell Save DC. If I choose that it changes in size and shape to fit the new form, its bonuses should still apply and lead to +8 and DC 16 accordingly, yes?

I don't claim to be an expert in abilities or powers that allow people to take the form and abilities of others. So I look at it from the perspective that the Adult Dragon is now the PC and you have automatically inserted your ASI's and what not in that creatures stat block. Those checks that rely on your added ASI are used and the ones that rely on the creatures, that are still available, are used. You get all of it's Immunities, Traits, Actions etc. It seems to me that the writers wanted these type of things to be simply done as possible.  Your magic amulet any other magic and non magic items conforms to the new form or drops off at your wish per the spell, and yes the bonuses are still added on. 

Quote from MPA >>

Quote from Disil >>

The Spell:

Shapechange: 

You shape-shift into another creature for the duration or until you take a Magic action to shape-shift into a different eligible form. The new form must be of a creature that has a Challenge Rating no higher than your level or Challenge Rating. You must have seen the sort of creature before, and it can’t be a Construct or an Undead.

When you cast the spell, you gain a number of Temporary Hit Points equal to the Hit Points of the first form into which you shape-shift. These Temporary Hit Points vanish if any remain when the spell ends.

Your game statistics are replaced by the stat block of the chosen form, but you retain your creature type; alignment; personality; Intelligence, Wisdom, and Charisma scores; Hit Points; Hit Point Dice; proficiencies; and ability to communicate. If you have the Spellcasting feature, you retain it too.

Upon shape-shifting, you determine whether your equipment drops to the ground or changes in size and shape to fit the new form while you’re in it.

 

The Question: If my level 17 Druid with 10 Int and 10 Cha uses Shapechange to turn into an Adult Gold Dragon, retaining these scores, what would be the spell attack bonus and spell save DC?

The statblock reads: 

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 21, +13 to hit with spell attacks)

My understanding would be that my Druid casts Guiding Bolt and Zone of Truth from the Dragon's Spellcasting feature not with +13 and DC 21, but with +6 to hit and DC 14 based on having a +0 modifier and a +6 Proficiency Bonus. Is this correct?

 

Added wrinkle: My druid has an amulet that grants +2 Spell Attacks and Spell Save DC. If I choose that it changes in size and shape to fit the new form, its bonuses should still apply and lead to +8 and DC 16 accordingly, yes?

 

I don't claim to be an expert in abilities or powers that allow people to take the form and abilities of others. So I look at it from the perspective that the Adult Dragon is now the PC and you have automatically inserted your ASI's and what not in that creatures stat block. Those checks that rely on your added ASI are used and the ones that rely on the creatures, that are still available, are used. You get all of it's Immunities, Traits, Actions etc. It seems to me that the writers wanted these type of things to be simply done as possible.  Your magic amulet any other magic and non magic items conforms to the new form or drops off at your wish per the spell, and yes the bonuses are still added on. 

Wouldn't having to re-calculate stuff based on inserted attributes run against your interpretation of things being done as simply as possible? Or are you saying that only skill checks are recalculated, but all abilities and spells on the stat block should remain as-is?