To get this one, you'll need to create a custom minifig (make sure you're creating a totally new minifig with the "add character" option) using parts from various different characters introduced in the Monsters DLC (no two parts should be from the same minifigure). You'll need a minimum of 4 or 5 to do this, but contrary to the achievement description, you won't need ALL of the new minifigs.
Here's the list of minifigures that count, if you need a reference:
*Make sure you're using all different pieces when you do this, meaning separate shirt and arms, and seperate "hip" and leg pieces!
Nearly of them can be obtained by simple means: doing quests and handing out items. However, there are two additional minifigs that can only be unlocked by other means (and you should unlock them for the Colour Me Spooked achievement anyways).
From the start menu, load your save file. The game places you at the galaxy map. Hit
to return to the actual "main menu" of the game. Scroll to right until you reach the "Enter Code" option. Enter the following code to unlock a new minifigure: x29vty
. You'll unlock this guy:
Now you can "buy" him in-game with the discovery tool, and you'll have more pieces to work with.EDIT: the Bat Monster is no longer obtainable as the model to unlock him has been removed from the main menu. Luckily all achievements are still obtainable, you won't need him to 100% the game!!
The second minifigure is obtained from the same menu as the previous one. You'll notice that a Lego model is being shown in the center of the screen. You can save these models for use in-game! Scroll to the right until you reach the " + " symbol. Select this to save the current model to your in-game inventory. You can scroll through them with and if you aren't interested in saving them all. The one you specifically want to save is the Monster Graveyard. Once you've saved it, load up your Monsters DLC world, find an empty space, and "build" the model using the Discovery Tool.
Once it's finished building itself, you'll notice a new minifigure hanging out inside. Step into the graveyard and give the Bat Monster a Red Apple. You can now "discover" him and use him for the achievements, too!