Get The Lightning Ring And A "Duplicator".
Level The Lightning Ring To Max, Then If You Have Been In The Level For More Than 10 Minutes -
The Next Chest You Open Will Evolve A Weapon That Is Eligible.
Eligible Weapons - A Weapon That Has Achieved Max Level, And It's Counterpart (Or Support Item) Is Also Equipped.
The Achievement Pops After The End Of The Run.
Good Luck!