This achievement requires that you unlock all upgrades in each of the three upgrade trees listed on the Waynetech page in the pause menu.
Most of them will be unlocked simply by progressing through the main story and purchasing them as you level up. However you will also be required to:
*Complete through challenge 10 of each of the first three Dark Night tracks
*Capture each of Black Mask's Assassins
...for which there are already a number of excellent guides.
Pay particular attention to the Worst Nightmare Dark Knight track. Many challenges can only be completed in particular rooms. It is easy to fall behind. Luckily you only need to run through challenge 10, not all 15.
You must acquire all upgrades over a single save game file. You may use NG+ and I Am The Night Mode to unlock any items you missed in your first playthrough. In general, if you are missing a particular upgrade even after achieving max level rank, just highlight over it and the game will provide the prerequisite.
Max level can easily be obtained within a single play through. Crimes in progress, collectibles, and miscellaneous street fights provide an endless supply of xp. That being said, I found it most natural to grab my last 2 or 3 levels while I played through ng+.
If you unlock your final upgrade during a later playthrough in which you have not yet acquired all of the story line upgrades (shock gloves) then the achievement won't pop until you exit to the main menu. For example, I didn't unlock the sonic batarang (via Worst Nightmare Dark Night track challenge 10) until I was in a NG+ run that had not yet progressed far enough to unlock the shock gloves. I got a checkpoint, exited to the main menu, and it popped moments later.