Black Gold is still a must have in Tower of Fantasy. SSR Weapons like Samir, Huma, Tsubasa, Zero, etc. are zero stars at the start and lack many of the abilities that will make them real terrors on the battlefield. With Black Gold, you can buy a duplicate and level your Weapon up a star for certain.
Earning and spending Black Gold
Every Gold Nuclei you spend to complete a gacha pull in the Standard Banner earns you a single unit of Black Gold. With those, you may purchase elemental cores, Nano coatings, and other upgrade materials. Or, you may purchase duplicates of SR and SSR Weapons you have already pulled for an increased charge.
Only spend your Black Gold on SSR Weapons. Every ten Gold Nuclei you spend guarantees at least an SR Weapon, and you're likely to have the six you need to upgrade a Weapon to maximum star rating just by playing the game and using Gold Nuclei.
Don't hesitate to upgrade your SR Weapons, either. If you pull one once it's maxed out, you get one Black Gold instead of getting more upgrades. The more maxed you have, the more Gold you'll receive for duplicate pulls, making purchasing your next SSR Weapon a lot quicker.
If you have the limited-time gacha event and earn Flame Gold, youll eventually be able to spend 120 units to guarantee the Nemesis Weapon. If you have any Flame Gold left over when the event ends, it will automatically be converted into an equal amount of Black Gold later on.