Does the Pyromancer sorcerer's Fiery Soul feature totally bypass immunity to fire damage?

Question

The Pyromancer sorcerous origin from Plane Shift: Kaladesh has a feature called Fiery Soul:

At 18th level, you gain immunity to fire damage. In addition, any spell or effect you create ignores resistance to fire damage and treats immunity to fire damage as resistance to fire damage.

This ability allows you to treat immunity to fire damage as resistance to fire damage... and allows you to ignore resistance to fire damage.

Does the "ignore resistance" portion of this feature allow you to also ignore immunity that is turned into resistance by this feature?

Note: This is not official D&D 5e source material. Rather, it is something like Wizards of the Coast's "official homebrew"; it's un-playtested material by James Wyatt.

Answer 1

No, it doesn't completely bypass immunity

When a feature is designed to ignore both immunity and resistance to a damage type, rather than "reduce/step down" one level of protection, it is quite explicit in this. One other class feature does this - the School of Evocation wizard's Overchannel feature:

[...] Each time you use this feature again before finishing a long rest, the necrotic damage per spell level increases by 1d12. This damage ignores resistance and immunity.

Here, the ability is clear that it ignores both immunity and resistance because it groups them together. In contrast, the Pyromancer's Fiery Soul breaks each step down and separates them, indicating that it only works to either change immunity into resistance or change resistance into regular damage.

Answer 2

No

Although the text is somewhat unclear, the lack of clarity points to the answer.

If the intention was for all immunity to be bypassed, it would be written something like

At 18th level, you gain immunity to fire damage. In addition, any spell or effect you create ignores resistance and immunity to fire damage

Instead, the text simply downgrades immunity to resistance, and any previous resistance is ignored.

Answer 3

The wording leaves a lot open to interpretation

There are two ways to read this ability:

1. Creatures with fire resistance are treated as having no resistance, and creatures with fire immunity are treated as having fire resistance. Essentially going down only one step in either case.
2. Fire resistance is ignored. Since immunity is treated as resistance, it is also ignored.

Due to what I see as ambiguous writing, either interpretation could be derived from the ability and it would be up to the DM to have the final say in how this ability works in their game.

It would seem to me that the intent here is for it to be treated as case 1, causing fire resistance/immunity to move down one step. If it were intended to cause both fire resistance and immunity to be ignored, it could have easily said so in fewer words.