Legendary weapons are hard to come by in Elden Ring Nightreign. They are exceptionally rare drops from defeating Field Bosses as well as the boss at the Castle location. Fortunately, there is a third avenue for you to acquire gold weapons.
This guide has everything you need to know on how to upgrade any weapon to a gold-bordered legendary for free in Elden Ring Nightreign.
Special Armament Strengthening
Whereas you would ordinarily use Smithing Stones and runes to upgrade weapons at a smithing table from one tier to the next, this process requires neither. It is, however, subject to certain in-game conditions that are random, so you may not necessarily be able to do it on every run.
The Crater Shifting Earth event must occur during your run. This event initially unlocks by defeating Gladius, Beast of Night. Once you undertake the Crater event, make your way through it until you finally defeat the Magma Wyrm final boss. You will find a Special Armament Strengthening table unlike the ordinary smithing tables you are accustomed to normally.
This Special Armament Strengthening table will upgrade any weapon, be it common (white), uncommon (green), or rare (purple), directly to legendary (gold) without needing to progress through any intermediate tiers. Moreover, legendary weapons created in this particular manner have no minimum level requirement, so you could potentially make use of weapons well before the usual requirement of level 10 for the rewarded legendary weapons that sometimes drop from bosses.
Unfortunately, you cannot upgrade more than one weapon to legendary per run, so make a careful and considered choice when doing so each time.
That is how to upgrade weapons to the gold legendary tier for free in Elden Ring Nightrein.