Figure

The toy Skylanders Figures are the key focal point in the Skylanders series, as they not only allow access to the Skylanders but also are the means to carry that data around and be shared with others. They are what truly bridges the gap between the home consoles, handheld devices, and even PCs. All figures do have at least one thing in common. All Skylanders of a particular element have an identical base (e.g. all Tech Skylanders are on a pile of gears).  Depending upon the kind of figure, the pedestal may be larger, but it is still basically identical. However, not all Skylander figures are the same. Different figures of the same Skylander can have different effects or abilities. As the series progressed, new kinds of figures were released with new abilities.

Skylander Figures can belong to multiple groups, though this is usually the case with Variants and Legendary Figures (see below).  For example, a variant of Drill Sergeant that is solid red that was released is both a Variant and a Series 1.

Also, for the sake of completeness, there is a listing for the other two figures that are not of Skylanders, Items and Locations.

Series 1

Series 1 figures were the original 32 Skylanders. They are identical in toy and game form, though some individuals do have slightly different details such as different colored eyes. They are all compatible with Skylanders: Giants and other Skylanders games.

Dark

There is currently only one Dark figure, Dark Spyro.  Dark Spyro is listed with the 32 Skylanders in the Strategy Guide, bringing the total to 33. In the console games, Dark Spyro is supposedly just like Spyro, but he is quite different from regular Spyro to the point of having a completely different backstory and 3DS moveset. Dark Spyro is essentially a Series 1 figure. 5 new Dark Skylanders, including Dark Ninja Stealth Elf, will arrive as exclusive figures in the Skylanders: Swap Force Dark Edition Starter Pack.

Legendary

Legendary figures are gold and navy blue versions of normal Skylanders. Their in game versions match the figures' color scheme, and are supposedly slightly more powerful than the regular versions. The original Legendary figures (Spyro, Bash, Chop Chop, and Trigger Happy) could considered Series 1, just like Dark Spyro.  However, those released with Giants (Stealth Elf, Ignitor, Slam Bam and Chill) are not backwards compatible according to the packaging. They are all commonly available only at Toys R' Us.

Variant/Rare

Variants are figures that are different in toy form only. They can be composed of all one color, for example there was a solid blue Bash.  Rare figures are variations that are impossible to find in stores, such as silver and gold Skylanders, even pearl.  One set of variants released for Giants are glow in the dark. However, though they all are colored uniquely in their toy figures, they don't share the color variant in-game.  As far as is known, these figures are simply altered versions of regular figures, whether Series 1 or Series 2, and their in-game version are the same as the regular version without any changes to appearance or ability. These should not be confused with Alt Deco figures, as they are called in the Giants Strategy guide, see below. 

New Character

The term 'New Character' is from the Skylanders: Giants strategy guide.  It applies to the eight new core, or basic, Skylanders introduced in Skylanders: Giants, though the moniker could apply to the Giants themselves.  New Characters are identical to Series 1, except that they are NOT compatible with older games.

Giant

Giant figures were released for the game, Skylanders: Giants. The Giants figures are much larger than the normal Skylanders, which is reflected in game as their game form is equally larger than a normal Skylander.  However, despite their size, but they function identically to regular Skylanders. Giants figures could also be considered New Character figures (just introduced) and like the Lightcore figures, parts of their bodies light up when on or near a portal (though they lack the Lightcore figures' ability). Like the New Character and Lightcore figures, they are not backwards compatible. Every time a Giant is placed on the portal, a dramatic yet heroic music is heard as soon as they appear in the game.

Series 2

Series 2 figures are new versions of the older Skylanders.  They depict the original Skylanders in different poses or with certain paths fully upgraded.  There are 24 Skylanders, three for each element. There are a few things that set Series 2 figures apart. First, according to the Giants Strategy Guide, Series 2 can alter their upgrade path, switching between the options without having to restart.  Second, Series 2 figures have an extra upgrade, the Wow Pow Power, which grants them an extra ability or boost above their Series 1 counterparts. Third, the Series 2 figures are backwards compatible, but the Wow Pow Power upgrade is unavailable or non-usable in Spyro's Adventure. As for the Core Skylanders originally debut from Giants will be backwards compatible only in the second console game.

Series 3

Series 3 figures are newer versions of the SSA Skylanders reposed in Giants with brand new Wow Pow abilities much different than their Series 2 versions. Also, their appearances are altered, such as Spyro's horns and tail become bigger and renamed Mega Ram Spyro or Stealth Elf starts wearing a black ninja garb and wields a new pair of blades. They will all be backwards compatible in Spyro's Adventure and Giants.

Swap Force Skylanders

Swap Force figures are toys that have detachable upper parts of their bodies to allow the Swap Force to use different powers and abilities than just their own.

LightCore

LightCore figures are figures with parts that light up when placed on the portal. This translates in game as a massive blast when summoned, knocking away or damaging nearby enemies. LightCore figures may or may not be backwards compatible. At least some of the packages say that they are not, even if they are of one of the original Skylanders, but some reports that those of the original Skylanders will work with Spyro's Adventure..

Alter Ego

Alter Ego figures are much like Variants. However, they are named and listed separatedly in the Giants Strategy Guide. There are two main differences between Alter Ego figures and Variant figures. First, Alter Ego figures are named, such as Punch Pop Fizz and Gnarly Tree Rex , both in game and out while Variant figures carry the name of the basic figure they are based upon. Second, Alter Ego figures are differently-colored versions of characters that appear inside the game as they are outside of it, i.e. the toy and game forms are identical unlike Variants who only appear different in toy form. As a final note, many Alter Ego figures are exclusive to certain packs or bundles, like Gnarly Tree Rex or Royal Double Trouble. Legendary figures, as stated above, are not Alter Ego figures because they are slightly stronger versions of the characters, not simply renamed pallete swaps.

Magic Items

Magic Item figures are the smaller figures that originally came in the Adventure Packs. They are mobile power ups, presumably able to cross over between games to give Skylanders a helping hand. They are smaller than normal Skylander Figures, so they can easily share the space on the portal. 

Sidekicks

Sidekicks are miniature versions of the original Skylanders. When placed on the portal, they say whatever catchphrase uttered by their regular counterparts. For instance, Whisper Elf shouts out "Silent But Deadly!" They don't do anything except follow Skylanders around.

Adventure Pack Figure

Location Figures are the figures that represent new maps. Originally, these were released only in the Adventure Packs. They unlock both a hidden level or area as well as a new battle arena while they are on the portal. 

Battle Pack Figures

Special magic items can not only be used as weapons against enemies, but also unlock new Battle Arena in multiplayer mode when placed on the portal.