Mato Anomalies

12 different types of legendary weapons refers to twelve unique items total. Having 12 legendary spears is not the goal. You want two different types per character.

For Gram: A sword and a spear.
For Butterfly: A dart and a claw.
For Smoker: A pistol and a spear.
For Mist: A curved blade and a wire ring.
For Lady: A shotgun and an uzi.
For Ringless: A rifle and a hand-blade.

My personal recommendation is to farm Random Lair 6-5 until you receive each weapon you need. This was how I earned the achievement. The drop rate for legendary weapons and gears are heavily accelerated in this area. I do not recommend post game or end game arenas as you’re reaching beyond meta/normal play.. instead of a higher quality weapon or increased drop rate they reward you with higher weapons all around. The cap of normal play is level 10 weapons. End game brings you up to 12+. 6-5 is your best bet as it’s the second appearance of legendary items being available and the last regular level set before they begin the climb to end game potential.

in addition to Vudix I would like to give a good tip, after you have defeated the boss of Random Lair 7-5 leave the dungeon without collecting the last chest the game will create an autosave while you are still in the dungeon load the auto save open the chest and if there is no new legendary weapon inside, simply load autosave again.