To beat the whomping willow try start by having Herimone cast the perticus totalas spell then have Harry cast the diffindo spell. This make take a few trys but it will work.

If I am right, remembrall is a charm, you cannot buy it from Fred and George, you can find these charm outside Hogwarts Castle where some toad/frog-like wander around. Go and touch the toad/frog and kill it, you will retreive a remembrall and some sickles.

To defeat him you have to use your most powerful spells. Do incendo or glacius.

If you can't find the wizard cards, try going by floor, like 1st, to 2nd, 3rd etc. If you can't find it that way try going to Fred and George's place. They have lots of goodies there!

After you have rescued Buckbeak, go to the lake and wait a few seconds and Hermione will howl and Lupin will come. In order to defeat him you must keep Buckbeak alive, and you keep Buckbeak alive by turning it invisible using the fumos spell. Dont waste any of your sp because none of your spells does very much damage.Notice that lupin only goes after Buckbeak.

Getting all of the wizard cards is very simple. While you're playing the game, make sure you collect all those treasures in the little treasure boxes. Some of them will contain cards, and some will contain sickles. Those sickles can be used in Fred and George's shop. Every wizard card in their shop costs a mere 5 sickles! Use up all of your sickles until you're left with nothing. Do this several times and you'll get all the wizard cards in no time.

After you've gotten all of your wizard cards, go to the Fifth Floor and in one of the rooms you can get rewards for collects groups of cards.