Gotham Knights

EDIT: If you quit to main menu after killing a most wanted criminal and picking up his loot , but before completing the crime, you can redo the crime while keeping your gear. I did the same one three times in a row just now and have 3 legendary crafting schematics and enough gold crafting stuff to make all three. Thank you to "Exactor it" for this. I didnt notice until "Gizmo 2k" brought this up and also 1 last thank you to "Gizmo 2K" so i could change the solution.

If for some reason that does not work for you... Keep reading. The next part is for you.
First of all the main ingredient you will need most likely will be Nth metal. Now there seems to be a couple ways to get this but the 2 ways to get them 100 percent that i found was.....
1: Do the penguin challenges and he will reward you with them Nth metal. Problem.with this is he only gives between 10 and 20 Nth metals.
2: find missions labeled very hard and look for the most wanted. The most wanted people only come out rarely on VERY HARD PREMEDITATED ONLY!!!
The only way ive seen to get them is to hold down on the digital pad to scan all the enemies in the very hard mission and when you see an actual name like Iron Knuckle or H!gh $c0re or Sick one instead of regulator champion or brawler or veteran. Once you see that name you know you got one. Killing one grants you between 100 to 200 Nth Metal.
There is also 8.2 main missions in the entire game. The last mission is called Lazarus pit. When you see this stop playing the main game and start farming for all the achievements you need. The only achievement you cant get is the max level because the level cap 1st playthrough is 30 and then new game + lets you get to 40 which is the real level cap.
Also...As Xaero Hour has said in the comments, it is indeed to get Nth metal now that the update is out. Search chests and beat stages to get this precious metal. I can 100 percent confirm this being that now I am at about 17,000 Nth metal. I have gotten easily 900 Nth metal out of 1 chest and if you go online and get more buddies this is easily accomplished. Thanks to Xaero Hour for bringing this up.