Here is a very good guide of the Skylanders taken from
Code:
http://www.gamepeople.co.uk/collecting_wii_spyro-skylanders.htm
Each of the toy figures belongs to a particular grouping: Earth, Fire, Air, Life, Undead, Magic, Water and Tech. Owning all the characters in one of these groups gives you an extra bonus when you play. Also, the groupings define how the characters perform against each other in the versus mode and in the main campaign. Each group has special areas that only they can access.
Earth Characters: Terrafin Prsim Break Bash Legendary Bash Dino-rang Silver Dino-rang
Fire Characters: Ignitor Eruptor Silver Eruptor Flame Slinger Sunburn
Air Characters: Sonic Boom Lighten Rod Whirlwind Warnado
Water Characters: Gill Grunt Zap Slam Bam Wham Shell
Magic Characters: Spyro Dark Spyro Legendary Spyro Voodood Double Trouble Wrecking Ball
Tech Characters: Trigger Happy Legendary Trigger Happy Boomer Silver Boomer Drobot Drill Sergeant
Life Characters: Stealth Elf Stump Smash Zook Camo
Undead Characters: Chop Chop Legendary Chop Chop Ghost Roaster Hex Cynder
When choosing which toys to collect you need to balance the benefits from owning all of one sat against the being able to pick and choose from the different sets and access more of the special areas. Also, if you are going to be fighting against friends you may want a range of different character groups to select from to match up against their toys. For instance, fighting Fire with Water is more effective than fighting it with Tech.
As well as these groupings. the toys each have a set of starting characteristics that defines how they perform initially and how you can power them up and upgrade them in the videogame.
Firstly, they have a primary and secondary attack that defines both the style, range and effectiveness against different enemies. The primary and secondary attacks can sometimes be used in combination to increase the power or reach of a weapons. For example Prism Break can fire his primary Beam attack into the crystals he summons with his secondary Shard Summon attack to reflect it in more directions and increase its range.
Secondly, each toy has a particular set of upgrades. Again these provide additional attacks that can increase the range and power of their starting weapons. These will either offer a new ability or power up an existing one.
Finally each toy has a set of characteristic stats that define how they perform. These are upgraded as you work through the different levels but still determine how powerful they can become.
The in-game stats detail Max Health (Hit points), Speed (Movement), Armour (How Hard to hit), Critical Hit (Chance of doing extra damage), Elemental Power (Increase effect of elemental zone), Heroics (Challenges completed), Hero Level (Website progress).
The cards/web game stats are slightly different. These detail Attack (the strength of their weapons), Agility (how high they can jump and how fast they can move), Defense (how much damage their armour and body will absorb from an enemy attack), Luck (how quickly they recover from stun attacks), and is used in other non-skill based aspects of the game.