LEGO Harry Potter: Years 1-4 Guide
Unofficial LEGO: Harry Potter Years 1-4 Guide by Vhayste for SuperCheats.com
This walkthrough is meant to assist players maximize their initial run. You can replay previously played chapters so don't fret about missing anything in your first playthrough. You will encounter locked paths, chests and objects but don't worry; the spells and characters you need can only be acquired late in the game so don't feel bad about missing them initially. This walkthrough will list the stuff you can backtrack as soon as you have the means to access them.
The same goes with crests; previously acquired crests do count so it means you just need to gather the other pieces again per story chapter. The walkthrough will discuss how to get the crests that you can access without the need of special magic or character. You need two vital things to unlock most of the stuff: the spell Reducto (RE) that can unlock silver locks, chests and gates and the dark version of Wingardium Leviosa called Crucio (CR) exclusive only to dark arts characters. Reducto is automatically learned after complete chapter 2 of Year 4 while the earliest dark character (Tom Riddle) you'll find is in Year 2, chapter 6. (Free play)
Another thing to note is that this game has some really annoying glitches that may prevent you from getting 100%. To be safe, I suggest keep a backup of your save game using a USB storage device of your choice. Its better to redo a few chapters than to do restart the whole game, if you're after getting all unlockables.
Finally, I am not a Harry Potter fan so excuse me if I don't know the common names of most of the characters nor the fancy terms used to call various stuff. So don't go emailing me correcting my spelling of their spells or telling me to change the names/ terms used in this guide.