Spoiler
To get this achievement you need to fish a Leviathan's Amulet from the corpse of a Water Elemental or Massive Water Elemental AND unrust a Golden Armor out of a Slightly Rusted Armor.
As the spoiler clearly says: You need to unrust "Slightly Rusted Armor", the Rusted Armor, Rusted legs, Rusted helmet, Rusted Shield and any other Rusted item aren't useful to get the achievement.
Why is this?
"That's almost too much luck for one person. If something's really, really rare - it probably falls into your lap sooner or later. Congratulations!"
I think that, what are you asking, is to know if there an easiest way to get this achievement, but I don't think there is one, it's meant to be for the luckiest ones. :c
Source:
https://tibia.fandom.com/wiki/Lucky_Devil