There's nice mechanical/industrial vibe to Avernus already in 5e. Infusing items with demons/sinners souls and crafting potion with demonic ichor could be awesome.

Winged Feral Tiefling
+2 Dex +1 Int

Background: Shipwright, you are specialized in crafting war vessels.

Class Artificer, Artillerist
- Use guns until level 5, at 5 use your arcane firearms to cast cantrips. Focus on fire spells.

At level 4 or 8, take Flame of Phlegethos, for a small fireshield when using fire spells, +1 Int and reroll 1s on fire spells.

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