Skylanders Giants

To get this, you must beat all Arena challenges once. You do not need to use the same skylander to beat them all, but you cannot switch skylanders mid-match.

There are 3 arenas, with 7 challenges each. Each challenge has a stated objective or battle effect and lasts for 3 rounds (with a few exceptions). In between rounds, you get a small breather and the crowd gives you food to heal yourself (unless doing challenge 7).

Completing a challenge gives a monetary reward to the skylander used and unlocks the next challenge. Repeating a completed challenge awards half the initial prize money. Completing the last challenge in a set gives you a charm that will effect all skylanders you use.

The challenges are:

Brock's Rump Roaster Ruckus (Unlocked after beating Chapter 3)
1) Stop the spell - Keep enemies out of the center
2) Smoke Screen - Smoke Bombs rain down on the arena. They can be destroyed to clear the air.
3) Cloudy Curse - You slowly lose health, but each enemy killed drops food.
4) Present Protector - Enemies will attack a pile of presents in the center stage; keep it alive.
5) Spell Dodger - Mortar attacks rain down as you fight
6) Force Field Frenzy - Enemies are invincible. You must knock them into the pit or the fire hazard.
7) The Perfect Game - You have 1 HP and cannot heal.

Completing these challenges earns you the Clever Clover, which gives you a chance to nullify attacks.

Kaos' Royal Flush (Unlocked after beating chapter 9)
1) Don't Beam Me Up! - Trogs (Green mummy things) will shamble toward beams. If left alone, they will beam up. If too many beam up, the challenge is lost.
2) No Chompies Allowed - Keep the zone cleared of enemies.
3) Fog of War - More smoke bombs
4) An Early Fall - Invincible enemies
5) Losing Ground - The floor drops fast and leaves little fighting room.
6) Sky Lasers - Another mortar one, but the blasts are faster.
7) One Shot Thrill - You have 1 HP

Completing these challenges gives you the Sparkling Sprinkles which increases health restored via food.

Pipsqueak's Mincemeat Mayhem (Unlocked after beating chapter 12)
1) Sticky Situation - Another mortar stage, but the blasts instead leave goo which slow you down tremendously.
2) Birthday Bash - Like Present Protector, but with cake
3) Trog Trouble - Stop them from beaming up again
4) Baaaaaad Idea! - Just like Cloudy Curse, but the drain is far more rapid. This has 4 rounds instead of the usual 3.
5) Bubble Blaster - Invincible enemies. This has 1 long round instead of 3
6) Icy Blast - Another mortar stage, but the blasts explode into giant ice crystals that block movement and attacks.
7) You Only Live Once - You have 1 HP

Completing these challenges gives toy the Bright Blade, which increases critical hit chance when at full health.

General tips:
1) Be patient. There's no time limit so don't rush in and take an unnecessary hit.
2) Focus your attacks. Concentrate on one enemy at a time to dwindle their numbers so you don't get swarmed.
3) Save your food. If you don't need the food they give you, leave it sit until you do.
4) Use an upgraded skylander. You need to be able to avoid attacks and kill enemies before they can attack. A level 1 fresh out of the box generally won't be able to do that.
5) If you collected the adventure packs from the first game, the powerups can be used in the arena challenges, making them a whole lot easier.