BattleBlock Theater

This may or may not be your first story achievement. I'll explain why....

If this is your first time ever doing the story it will automatically put you in the opening sequence (I recommend watching the video for hilarity's sake). Once completing the tutorial/sequence you will get the achievement and an avatar prop.

If, like me, you were part of the beta and participated in the redone second beta last week, even with deleting ALL of the beta information including saves, the game kept my progress in the story mode for normal play. If this is the case for you as well, you will not be able to start in the opening sequence on normal. Do not fret though. All you need to do is start a game on insane mode (assuming you didn't do that on the beta) and you WILL start in the opening sequence. follow it till the end and achievement plus avatar prop are yours.

If you did play in both modes on the beta (which I didn't) I do not know how to reset your stats or progression or even if it is possible. I will look further into it and update when I know more.

(Edit) I have learned that if you join a friends game that is just starting this you will play through their opening sequence and still get this achievement. I have yet to find any sort of story reset option, or hear anything from the behemoth about this issue. (I emailed them within minutes of writing this guide)

I hope this helps, even though I'm sure a vast majority of players won't even need this guide to get it.

Just start the game up, pick a difficulty, and watch the opening video (You can skip it, but I highly recommend watching it). Then just run through a few rooms, and then BOOM achievement unlocked.

In order to unlock, boot up story mode in local mode, pick a difficulty (I recommend normal, this game gets quite hard at times) and watch the funny intro sequence. This achievement should unlock as soon as you gain control of your avatar.