I'm adding a version of the UA Phoenix Soul sorcerer to my homebrew stuff, and I'm a little perplexed when it comes to adding damage for Mantle of Flame.
The relevant text of the feature reads:
Any creature takes fire damage equal to your Charisma modifier if it hits you with a melee attack from within 5 feet of you or if it touches you.
Whenever you roll fire damage on your turn, the roll gains a bonus equal to your Charisma modifier.
In trying to add both of these features, if I select Modifier Type "Damage," then there doesn't seem to be an option to add a character's Charisma modifier. If I select Modifier Type "Bonus," there's a Charisma modifier option, but there doesn't seem to be a way to indicate it's damage.
How do I proceed?
This is probably all very obvious and I'm missing something right in front of my face, but I'd love some guidance.
Best Answer
There probably isn't a good way
I'm definitely not an expert on D&D Beyond's homebrew creation system, but by comparing to the closest working option I could find hasn't provided a working option.
The Bracers of Archery provide a +2 to damage from Shortbows (among other benefits). This is automatically added to the damage roll right on the character sheet:
The Modifier for the damage bonus looks like this:
If we remove the "Fixed Value: 2" and add "Ability Score: CHA" like so:
Then the Shortbow damage receives a bonus equal to the Charisma modifier, which is good other than being a Shortbow:
Going back to the item, we can change the subtype from "Shortbow" to "Fire":
However, when we look at the character equipped with the newest custom item Fire Bolt has not received the damage bonus:
There isn't any other Subtype that seems remotely applicable, so this method sadly does not work for your purposes.
If they add the functionality later, it might be done as a Subtype of a "Bonus" modifier, which seems to be how the Cleric's Knowledge Domain subclass and the Warlock's Agonizing Blast invocation are implemented, but no appropriate option is currently available:
You can manually adjust individual spells to give them the bonus damage if you want, but from my tinkering there isn't a way to make that bonus adjust with Charisma changes, or a way to have that adjustment applied based on the damage type, so it's probably more convenient to just keep track of it yourself.
For the other feature I don't think there's really anything for D&D Beyond to even do. There isn't a roll required or any D&D Beyond feature for determining what things activate when you are hit with an attack, so it will be up to you to track it regardless.