You can find extra Crests after completing Harry Potter's adventure. At some places in Hogwarts you can find firework boxes. Burn these with Incendio to make them explode. A broken Crest will pop out. Repair it with Reparo and pick it up. (For instance, check out the box nearby the duel club of Hufflepuf).
Playing match is pretty easy. You must fly through all the stars in the sky to catch the snitch. Passing all stars is not required if the star's color is going from red to light. This means that your time is coming to an end, so try to pass through most of the stars in the sky.
Find the crest you want to knock down and cast Wingardium Leviosa on the object you want to use to knock it down. Note: This object can be anywhere and does not have to be in throwing range of the crest. Using either a Dung-bomb or an Exploding Cauldron is recommended. Once the object is in the air, hold [Run]. You can now walk around the castle and grounds while still carrying the object in the air. Make sure that you keep [Run] held until you get to where the crest is located. Note: During this time Harry will not run fast. Throw that object at the crest to knock it down.
Collect the listed number of Hogwarts Crests to unlock the corresponding bonus.
CRESTS - BONUS 3 hogwarts crests - Two Player Dueling Pack 1: Draco and Luna 8 Hogwarts crests - More health in duels 14 hogwarts crests - Two Player Dueling Pack 2: Training Ground Dueling Arena 21 hogwarts crests - Dungbombs in prank boxes around Hogwarts 29 hogwarts crests - Two Player Dueling Pack 2: Crabbe and Goyle 38 hogwarts crests - Score boost in flying events 48 hogwarts crests - Exploding Cauldrons in prank boxes around Hogwarts 59 hogwarts crests - Two Player Dueling Pack 4: The Transfiguration Dueling Arena 71 hogwarts crests - Even more health in duels 84 hogwarts crests - Two Player Dueling Pack 5: Ginny and Hermione 98 hogwarts crests - Love Potion in Potions Club 113 hogwarts crests - Two Player Dueling Pack 4: Paved Courtyard Dueling Arena 129 hogwarts crests - More mini-crests with each cast Easy duels: Cast Levi Corpus or Petrificus Totalus, then charge your Stupefy until it chimes twice and release it. This will results in a one hit kill. This does not work for Fenrir Greyback.
You can get a large amount of Mini-Crests after using the Luck Potion and you are making your way to Herbology. At this point, every time you use Diffindo to get the Mini-Crests to appear, you will get the full amount of Mini-Crests available, due to your luck. Get as many as possible at this point to help reach the 25,000 pieces goal.
-To easily win pretty much any fight or duel,cast Levi Corpus or Petrificus Totalus. Then just charge your Stupefy until it chimes twice, then release it. It will result in a one hit victory until later in the game, then it will require two. Note: This does not work on Fenrir Greyback.
-Use the following combo to easily defeat any enemy. Use Expelliarmus to knock them down, then charge up your Stupefy. While getting it charged, walk next to your dueling opponent and fire your charged Stupefy for a one hit kill. This trick can give you 5 stars for the challenge very easily.