I am in the very end of BL2 and obtaining its achievements. Spent some time in it grinding for the 2 achievements I got today.
In the Hammerlock's Hunt DLC I had to run around and kill few specific animals that only spawn in some specific areas on random intervals and not so commonly. Well, Google is our friend and I found instructions, what areas to check, and then do the classical "load your save game, run around, kill animals, save, quite and repeat".
The "Challenge Accepted" achievement was even more bizarre. For it to be unlocked, you have to have "Completed level 1 of all non-level-specific challenges with a single character". The problem is that 2 of the level 1 challenges become only available after you get level 5 in two other challenges. I was stuck of getting 750 point blank kills with shotguns, as it just is not my gaming style. I am more sneaky sniper kind of guy who uses turrets or grenades or rocket launcher to get rid of enemies form distance.
NB, there are some BL2 shift codes available.
Xbox 360 SHiFT Code for 3 Golden Keys in Borderlands 2:
W3KTB-3BH5T-9R93F-WRB3B-SZBZR [Active through 10/29]
Then I played a little of Jetpack Joyride, but got no achievements there. Last but not least, did my "daily" moves in Win 8 AlphaJax and got one easy (just time consuming) achievement there.