I recently visited an ancient anvil with my never used flame sword that I forgot the name of and a drill spear that I spent hours on grinding for. The flame sword appeared in the anvil's upgrade list but the drill spear didn't… I really like the drill spear and I would love it if I could upgrade it at the ancient anvil. I think there are more legendary weapons that can't be upgraded but most of them are a little weird and they don't really need upgrades.
