Charms are collectibles in Skylanders: Giants. There are eight charms in total. They can be purchased from Auric or by beating Brock's arena battles. Each one has special powers.
Charms also made a reappearance in Skylanders: Swap Force where they can be purchased at Tuk's Emporium. However there are many more available than in Giants and all now have more minor effects on gameplay.
List of Charms in Skylanders Giants
Elemental Elixir Charm: Skylanders gain more health in an elemental gate area of their element. This can be purchased in the chapter 3 store.
Brawny Barbell Charm: Giants can lift boulders faster. This can be purchased on the Dread-Yacht after Chapter 5.
Sudsy Soap Charm: Attacks do more damage on troll enemies. This can be purchased in the Chapter 8 store.
Unerring Arrow Charm: Attacks do more damage to large enemies. This can be purchased in the Chapter 11 store.
Robot Repellent Charm: Attacks do more damage against robot enemies. This can be purchased in the Chapter 14 store.
Clever Clog Charm: Skylanders are more likely to deflect shots at low health. This can be obtained by beating Brock's Rump Roster Ruckus arena in Brock's Arena Challenges.
Sparking Sprinkles Charm: Skylanders get more health from eating food. This can be obtained by beating the Kaos' Royal Flush arena in Brock's Arena Challanges.
Bright Blade Charm: Skylanders are much more likely to score a critical hit at full health. This can be obtained by beating Pipsqueak's Mincemeat Mayhem in Brock's Arena Challanges.