To gain this and the other (Secret) L33T achievements you must get each stat up to 1337. It is best to do this on your first run through or on your last. I personally did it on my last run through since I didn't know about it on my first lol. If you're like me and save this one for last you'll need to reset your character after you get all the other achievements. If you play it this way and save it for last, go to Settings and press the skull button. This will give you a prompt on whether you're sure you want to hard reset your Idle Hunter and get set back to square one where you started. Choose Yes if you are ready.
Whether you do this on your first run or on your last after resetting your character you are now ready to try to get this achievement and the other hidden ones. You will naturally start off only being able to train your Agility Skill. Get it to 1337 and stop there. Then begin gathering wood and iron, you will need to build at least one Critical Hit building to kill the 1st level monsters to get gold. After you have a Critical Strike or two (I got it to level three just to play safe), start hunting until you get enough gold. Be sure you buy only 1 upgrade for Armor and Attack. This is very important so that you only train up 1 skill at a time and can precisely get 1337 stats in them. Then train your Attack and Armor up to 1337 as well. Once you have either one completed hunting will be easy to get gold for the last upgrade to the other skill. Buy only 1 upgrade for either Armor or Attack, whichever is the last to get to 1337 and make that 1337 as well.
Note: Be sure as you get close to 1337 to pay attention to the game, you must be at exactly 1337 skill, not over or under to get the achievement!
Now an issue you might run into is that when you initially get to 1337 in a skill their achievement does not immediately pop up. Simply stop the battle timer, exit the game, reload the game, and the achievement for that 1337 skill should pop up when you re-open the game. On the last one of the three skills at 1337 (and be sure the other two are 1337 as well) and you exit and re-open the game, the corresponding stats' 1337 achievement should pop as well as this achievement for having all three skills at 1337.
Happy Hunting, praise Jesus!