The Binding of Isaac: Rebirth

Update: This achievement is for fully completing the BASE GAME. If you have any of the dlc installed, it will make it a bit harder since some items have harder ways to unlock, like Godhead, and there's more items in the item pool so it'll probably take longer to find just the items from the base game. While I highly recommend getting all the dlc, if you're super focused on getting every achievement, completing the base game first will make it a little easier on you.

100%ing the game consists of 2 parts: seeing every ending and picking up every item. Your ultimate goal is to completely fill out the items, endings, and secrets pages under "Stats" on the main menu.

There's no real going out of your way for the endings, you'll get them as you play through the game, except for one that takes a little more effort.


Now for getting all the items in the game. First, you have to unlock them all.
Each of the challenges unlocks an item. For tips on how to unlock/beat them, check here: http://bindingofisaacrebirth.gamepedia.com/Challenges
Aside from that, you will need to beat every boss and clear boss rush with every character. You can easily track your progress on the character select screen. On the top left, you will see this box:
The symbols appear as you beat the corresponding boss with a character:

Only The Lost has to beat all bosses on Hard Mode, everyone else only needs to beat Mom's Heart/It Lives on hard to unlock a co-op baby for each. (do not even attempt to play as The Lost on Normal Mode as it will not unlock anything)

So, now you've manged to unlock all the items in the game. Now what?
Picking them up of course! Head on over to the Items page under Stats on the main menu to see everything you've picked up at some point. Anywhere you see a question mark, you haven't found that item yet. You can use this page to figure out what you are missing: http://bindingofisaacrebirth.gamepedia.com/Collection_Page (click on an item for more info)

You will also need to become both of the game's transformations at some point.
Guppy: http://bindingofisaacrebirth.gamepedia.com/Transformations#G...
Lord of the Flies: http://bindingofisaacrebirth.gamepedia.com/Transformations#L...

You will ALSO need to create level 4 Meat Boy and Bandage Girl. These are probably the toughest and most annoying things to get. Tips here: http://bindingofisaacrebirth.gamepedia.com/Cube_Of_Meat (works the same for Ball of Bandages, Famine will randomly drop either Cube of Meat or Ball of Bandages, and the rest of the horsemen will also drop the same for the rest of the run (except Conquest because he is a jerk)) Getting a level 4 Bandage Girl also unlocks The Bandage.