How can I increase the proximity damage from Ashardalon's Stride?

Question

I'm looking for a way to increase Ashardalon's Stride damage. The difficulty is that it is automatic and not targeted damage, and it affects multiple creatures as you move past them.

When you move within 5 feet of a creature or an object that isn’t being worn or carried, it takes 1d6 fire damage from your trail of heat. A creature or object can take this damage only once during a turn.

You can of course level up the damage by using a higher spell slot.. but Id like to pump it up more if possible.
Using only the official WotC printed rule books, are there any class abilities, feats, spells or magic items that might increase this damage?

Answer 1

Ready your movement for their turn.

Readying lets you choose movement as your response, using your reaction (PHB p.193):

[Readying] lets you act using your reaction before the start of your next turn. First you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it.

And depending on your chosen trigger, it can happen on someone else's turn (PHB p.190):

A reaction is an instant response to a trigger of some kind, which can occur on your turn or someone else's.

If you move past someone on your turn, and then move with your reaction past them on someone else's turn, those two events happen on different turns, which allows them both to deal the damage.

The downsides are that this takes your action, which is a hefty cost, and that a poorly chosen trigger might happen when your target(s) aren't in good position for you to run past them all. A badly chosen trigger might even not happen, wasting your action completely.

Answer 2

Sorcerer

Empowered Spell - this metamagic ability allows you to reroll low damage dice. Not exactly what you want, but useful.

Elemental Affinity - Under the Draconic Bloodline origin, this class feature lets you add your CHA bonus to the damage of spells that do a specific damage type. Ashardalon's Stride does fire damage, so if you pick the right dragon type (i.e. red or gold), you can add your CHA bonus to the spell.

Spell Bombardment - Under the Wild Magic origin, this lets you get an additional die of damage, if any die you roll has the max value (so roll a six and get more damage). This is an 18th level class feature and is kinda random.

Feats

Elemental Adept - Select this feat with the fire option and your fire spells do a minimum of two damage per die and ignore resistance. Again, doesn't increase the max damage, but good to increase the overall damage.

Spells

Contagion - The Flesh Rot variety of this fifth level spell gives the victim vulnerability to all damage. But you would have to get a cleric or druid to cast it, or get a magic item the inflicts it.

Geas - Another bendy answer, but you could geas a target with the instruction "don't get burned", then the next time that creature takes damage from Ashardalon's stride, they also take the 5d10 psychic damage. If you are a wizard using stride, you could also know geas, otherwise you need to get someone else to cast it, like contagion.

Glyph of Warding - put explosive runes on yourself with the trigger "inflict damage with Ashardalon's stride". Warning, this will damage you, too.

Hallow - can also give energy vulnerability, but it is more of a defensive spell.

Web burns for 2d4 damage to anyone in the same square. But a strict reading of web and Ashardalon's stride would seem to indicate they don't mix (stride damages creatures or unheld items, webs may not qualify if they are in the square with a creature). Your DM may or may not allow it.

These are the only options in the PHB and Fizban's, which are the only two books I have onhand at the moment.

(might want to make this a community answer).

Answer 3

Manage to get a Dragon Touched Focus from a Chromatic Dragon's Hoard.

Beside the inclusive list provided by Xavon_Wrentaile in their answer, there is also an option from Fizban's Treasury of Dragons that may help in what you desire: a Dragon Touched Focus belonging to a Chromatic Dragon's hoard.

A Rare Focus allows you to add a further d6 to the damage of a spell dealing cold, fire, poison, lightning or acid damage: since Ashardalon's Stride deals fire damage, it can benefit from this property.

A Legendary Focus allows you to threat the spell as it were cast using a 9th-level slot, allowing hence you to deal 7d6 + 1d6 fire damage (the further d6 is given by the Stirring property).

More details are listed below.

This wondrous item can be a scepter, an orb, an amulet a crystal or another finely crafted object. It tipically incorporates imagery of dragons' wings, claws, teeth, or scales.

[...]

Stirring (Rare). The Stirring focus has the Slumbering property, and it gains an additional property determined by the family of the dragon in whose hoard it became Stirring:

Chromatic. Whenever you use a spell slot to cast a spell that deals acid, cold, fire, lightning or poison damage, roll a d6, and you gain a bonus equal to the number rolled to one of the spell's damage rolls.

[...]

Ascendant (Legendary). The Ascendant focus has the Slumbering, the Stirring and Wakened properties. In addition, when you cast a spell of 1st level of higher while holding this focus, you can treat the spell as it were cast using a 9th-level spell slot. [...]