Overview
-Estimated achievement difficulty: 4/10
-Offline: 50 (1000)
-Online: 0 (0)
-Approximate amount of time to 1000: 10+ hours
-Minimum number of playthroughs needed: 2
-Number of missable achievements: 0
-Do cheat codes disable achievements? N/A
-Does difficulty affect achievements? Yes
-Glitchy achievements: None
-Unobtainable achievements: None
-Extra equipment needed: None
Introduction
This game is a quick and easy 1000 but it does have a few frustrating moments. You will need to play through the campaign twice because you need to complete the game on normal or advanced difficulty to unlock expert difficulty. I recommend you play on normal difficulty first because the difficulty achievements do stack so completing the game on expert will unlock the advanced difficulty achievement as well.
Step 1: Normal Playthrough
Start a new game on normal or advanced and simply play through the story. It should take you around 4-5 hours to complete it. Follow this collectible guide for the collectibles. Also make sure to kill enemies in certain ways to get the kill related achievements. You may get the achievement for killing 1000 enemies on this playthrough but I didn't so don't despair if you don't either because you still have to play through the game again and challenge mode so you will get it then. I would recommend the first level for the "Not a Scratch" achievement.
Step 2: Challenge Mode
I recommend you do challenge mode before your expert playthrough because you learn a lot of useful stuff while playing through the challenges. Challenge mode is basically a time trial of the story levels. Most levels are the exact same length as on story mode but some are shortened. Make use of the Impedimenta spell because you can use it to take down multiple enemies from afar easily. You only need to get gold medals so you don't need to worry about the platinum medal time. The only Challenge I struggled on was Challenge 7 'The Lost Diadem'. For this challenge Apparate towards the guys where you need to make the junk fall on them. Here is a video guide for the challenges. See the achievement guide for more tips on these challenges.
Step 3: Expert Playthrough
Now that you have completed the game once and completed all of the challenges with a gold medal this playthrough should be a doddle. Simply use Impedimenta on every enemy you come across and use cover as much as you can. This playthrough should be substantially quicker than your first playthrough now you know what to do. Also if you haven't done so already pick up the collectible you couldn't get earlier on in the 'The Streets of Hogsmeade' level.
Conclusion
You may still have "That Showed Them..." and "Stopped in Their Tracks" still left to get, so refer here for some great locations on where to get them. You may also need to get some collectibles or kills you have missed but you can replay the levels to get the kills or collectibles you need. You should now have all the achievements, well done.
x360a would like to thank jamie1000013 for this roadmap