Ben 10 Omniverse

This is best achieved after you complete the game.

Do a level select and choose "That was then". After you hit the first checkpoint, there are two repositories in front of you. Open them, commit suicide. Rinse and repeat and this should not take you more than 10 minutes.

You don't need to replay the game to get this achievement. As long as you hit a check point and then open one, you can suicide and restart and keep opening the same one over and over again. I forgot what level I did this in but it only took me 5 minutes due to the fact of there being 4 containers after my check point. You can use this restart trick with enemy kill achievements also.

In case anyone was wondering there aren't 75 repositories in the game. You can recollect repositories that you have already gotten, so you will need to replay around 5-6 more levels after you beat the game to unlock this. Just play on easy and it only takes around 10-15 minutes a level.

EDIT**** Thanks to Hexa Fox-- Apparently you can just replay any part where you know there are few and just grind out the same ones... You do not have to collect 75 different ones. But if you want to find them all....

Most of these are really easy to find however there are a few that are hidden, sort of. Here are some of the ones you may miss if not careful...

In The Galvanic Butterfly Effect, you will be fighting a bunch of guys in a room with 3 railroad tracks laying side by side. When you leave the room make sure to turn right. I missed this one the first time I went through it.

At the very beginning of Future Mal-Formed, you will pass over a bridge and drop down with Four Arms. Make sure you come as far as you can toward the bottom of the screen. This one is easy to miss.

In Extreme Earth Makeover, close to the beginning, you will jump up and climb with Four Arms. Make sure you check to the left before dropping down to the right. If you drop down on the right you wont be able to get back up. I also, somehow, missed this one the first time through.

Thats it. All of the others are either right in the path or behind puzzle doors. This game is easy too because you can just replay any mission. Happy Hunting.

As first post said, but the dummies guide for Open Season achievement :)

After completing the game, went
 CONINUE > START > SELECT LEVEL > "That was then..."
which is 7th level. 

Complete the initial battle, in which you can now change difficulty to easy as you have completed hard achievement already.

Go to where Forearms jumps up to climb,
There is a checkpoint here,
but INSTEAD go to right. 
Next to the deck are 2 Repositories.

Grab and jump in water and repeat. Took me 15 pick ups to get achievement. Had been picking them all up in game though, not just the collectable ones.