Harry Potter and the Chamber of Secrets/Spells and potions

Flippendo
A basic projectile spell that is gained at the start of the game. By pressing psx: S Harry sends a blue beam out of his wand knocking back items or enemies. This is used most frequently during combat.

Lumos
A spell learnt in Knockturn alley this gives out a green light from Harry's wand, this can be used as a light in dark places — useful for walking in the grounds on night time excursions and for fighting 'Gytrashes' (ghost wolf creatures).

Diffendo
A severing spell that is learnt on the first night at Hogwarts, the spell is found in greenhouse III and is used to cut tapestries and curtains in the game to find hidden passageways and of course free Neville.

Expelliarmus
A deflecting spell useful in duels with Slytherins and gargoyles! It is learnt on day 2 in Defence against the dark arts class.

Skurge
(all versions except PS1): Clears Ectoplasm (an "unpleasant greenish substance left behind by certain ghostly beings", in the words of Professor Flitwick) out of doorways and off floors. Harry may learn this spell in Charms (PC version), or during a late-night adventure in Hogwarts (PS2/Xbox/GCN versions).

Avifors
This is a spell that transfigures large eggs into birds; there is an egg in the library to transfigure at some point also. Learnt in transfigurations class.

Incendio
This is the fire charm which is learnt in charms (day 4). It's used for destroying webs and spiders and can open a door in the library.

Alohamora
This is the opening charm used to open chests with large gold locks (not for opening locked doors)! This is an extra and is not essential to game play however it's useful if you want to collect all the wizarding cards. Bought from Fred and George's shop costing 100 beans.

Wiggenweld Potion [stamina]
Harry learns, in Potions, how to make a Wiggenweld Potion, which replenishes his stamina after he's been injured. The ingredients are as follows, in the correct order:Flobberworm mucus Wiggentree Bark. In the PS2/Xbox/GC version however, Harry simply has to own one or more potion vials, and refill them with Wiggenweld Potion from Cauldrons or Dead Wiggentrees.

Polyjuice Potion [changing physique]
Harry also makes a Polyjuice Potion, and has to gather the ingredients Bicorn Horn, Boomslang Skin and "a bit of Goyle". The potion turns him into Gregory Goyle. however in the PS2/Xbox/GC version Hermione makes the Polyjuice Potion for Harry, on her own.