I want to get the "Challenge Accepted" achievement, but Shotgun and Launcher categories show an (undiscovered) challenge each.
These are the only two challenges that require rank 5 of another challenge to unlock.
Shotgun Sniper - kill 10 enemies with shotguns from long range
Catch-a-Rocket - kill 5 enemies with direct hits from rocket launchers
Good news is - all long range and direct hit kills done before unlocking these challenges still count.
You don't need to do these challenges for the "Did It All" achievement but you need them for the "Challenge Accepted" achievement. "Did It All" is completed by finishing all the side missions in one playthrough, so every mission not including the story missions or any missions in the downloadable content. "Challenge Accepted" requires you to finish rank 1 of all of the normal challenges including the ones that he provided and killing Jimmy Jenkins which I recommend doing when you go to do "The Doctor's Orders" quest as the he has a higher spawn rate during it and you can reload at the Natural Selection Annex to keep on trying for him. If you don't, you might find him purely by luck. Good luck!