How many 2012 Goodie Bags do I need to open to get ALL the tiers for that achievie?

Yup, that's it, thanks! :D

In relation to what...? Achievements? Items?

There are 18 items in those bags but what you get is random so you'll probably need to open more than 18.

The top achievement tier is 100 and there are 5 tiers under that.

Oh, yeah, achievements. Thanks.

Sorry, brain's fried today D:

I had to write this stupid essay, and read a whole diary in one sitting... Not fun...

Ah I edited my post based on my best guesses on what you meant. :)

2012 Goodie Bag Opener

Open ___ 2012 Goodie Bags! 1 5 10 25 50 100

From here.

Oh, thanks. That summed it up great!