Get Infinite Potion Ingedients:
During or after(after is the best) the Herbology lesson, Professor Sprout tells you to find herbs for an assignment.You an find an herb or ingredient,press 'A' to recieve it, press 'Start',press 'B' and recieve the item again!
Gain tons of House Points:
You can(while doing the Herb assignment) go back and forth between Hagrid and Sprout's,you need the fangs first though, talk to Sprout, gain 1 House Point, and continue this by going to Hagrid's, then going to Sprout's.
After you beat the game (the game restarts), to get all your spells back at the maximum level, get into a battle and use the card combination "Enchantment". It should be the last combination that you have.
After successfully completing the game, use the card combination that Dumbledore gave you at the end of the game at the first battle you encounter. It will give you all spells and allow you to keep them for every future battle.
All card decks:
To get all the card decks from the beginning of the game, defeat Voldemort four times.
Full Incendio spell:
In a battle, select "Spell", then "Incendio Tria". Then, press Left. The spell will now be targeting all of the creatures. Note: This spell does less damage than if done on one enemy.
The bonus games are Chase Draco, Catch Norbert, Get The Golden Key, Copy Flitwick, Potion Mixing, and Cards Match games.
Getting Norbert away:
When it is the night to give Norbert to Charlie's friends, go to Hagrid's Hut, then go back up to the seventh floor. Go past the mini-hallway to the picture of the Pink Lady and go into the next door on the left,. Go through all the corridors, and go up to the top of the tower. You cannot do anything about forgetting the invisibility cloak. Once Norbert is gone, just leave. There is nothing you can do about losing house points.
Easy level up:
Go to the hospital wing. If you are injured, talk to Madam Pomfrey. She will heal you completely. Then, go to one of the rooms beside or above Madam Pomfrey. Fight as many people as desired. When you get hurt badly, return to Madam Pomfrey to get healed. Repeat this as many times as desired.
Lose all of your House Points:
When you get to the part where you need to find the trophy room to duel Malphoy, go to the fourth floor. Note: Sometimes she is on the third, fourth, or fifth floor randomly. There will be an old lady standing watch. Talk to her twice. The second time she takes away one House Point. She keeps taking away one House Point every time you talk to her.
In the restricted section in the library, there are three vertical bookcases. The first one has a spell called Mucus Ad Naseum, which is useful when defeating the Devil's Snare towards the end of the game.
Stand in front of a piece of grass where you get herb plants. Pick it up, go into your menu, and exit out. More herbs will appear there.
Get rid of your curse:
Go to the Muggle Studies classroom, on the fourth floor corridor on the left side. In the top-right corner there is a "TV" thing. Press A in front of it and it will lead you to a secret room. Fight the monster inside. After you defeat him, you will get a curse book. Find it in your items list and select it. It will automatically heal you. Afterwards, you have to take the book to the library.
Quick items from bushes:
You can get items at the strange bushes very quickly. Press A then enter the start menu. Exit the menu and press A again and another item will appear.
To get Incendio, go to Professor McGonagall's class on the first floor and catch the rabbit to learn it.