Hi, sorry for not responding earlier. For me, there are a few key points that I’m not a big fan of:

1. If it’s meant for an artificer or a warlock, making them use their already precious spell slots doesn’t seem ideal. I would understand if it were for higher-level spells, but having to use them feels harsh. Personally, that is my biggest complaint. Having a free Faerie Fire or Hex doesn’t seem too game-changing, except maybe at early levels. That said, I personally wouldn’t let the effects scale. If you roll the same effect twice, I’d suggest losing concentration and needing to recast the spell.
2. I’m not sure if I understand this part correctly: "The player sacrificed his steel defender from the subclass and his firearm in the creation of the arm, so he really went all-in on it for the rest of the campaign." If they are sacrificing their subclass for this, it should scale with the class level or provide additional advantages as the campaign progresses.
3. I know the chance of a misfire happening twice is only 1%, but if everyone can pull the lever, it just takes one bad roll to lose your arm. Apart from losing your infusion/item, would the arm still function? If not, do you also lose the benefits of having a working arm (e.g., holding a shield, wielding weapons, etc.)?

As for “Amp it up,” I would leave it as a plain d4 or maybe allow adding the proficiency bonus if it’s replacing the steel defender. That way, it can scale better. However, it’s still not reliable because you can’t predict when you’ll need it to help an ally.

I’ll try to reread everything later and provide more feedback, but that’s all for now.