This game uses the 3DS IR port.
The 3DS version of Skylanders: Spyro's Adventure is a whole different game from its home console brethren. Developed by Vicarious Visions, Skylanders is more of a 3D platformer than the action game that the Wii version is. For example, there is no jump button in the Wii version, but there is one in the 3DS version (and a double jump as well).
Skylanders is a toy-based video game, as in you use specially designed toys that you put onto a "Magic Portal" to bring them into the game. Each copy of the game, retailing for $69.99, comes with the game, the portal, and three figures. The figures are different from the other versions, including Dark Spyro, Ignitor, and Stealth Elf. In the 3DS version, you place the characters on the portal, and then go to a specific in-game character, who allows you bring up to two characters into the world using the IR port on the 3DS. As far as I know, that's the first in-game use of the IR port on the system. These characters then display on the touch screen, and you can switch between anytime you want, even in mid-jump, by tapping the touch screen.
You can level up these characters, customizing their abilities and appearance along the way. If you wish, you can even bring them into any other version of the game and get more items and experience. Since the 3DS game is different, you could take your favorite character through two completely different games with varied play styles.
The goal of the game is to complete levels to get crystals, which then unlock more levels. That unlock method, and the general overworld design, is very similar to Super Mario 64. The way you get the crystals, though, is a little bit different. In each level, you get one for reaching the end of the level, but there are numerous other objectives littered throughout the level. They range from "Find 5 of these items" to "Defeat this many enemies."
When you complete an objective in a level, you awaken an enemy who chases you throughout the stage. A timer displays on the screen, and if it reaches zero, you lose. You can ward him off by defeating enemies and picking up rockets, which slow him down. It's an interesting mechanic that amps up the pressure after you complete an objective.
Vicarious Visions commented a bit on their development process during the game, and mentioned that they took the Wii assets for the game and improved them, which seemed kind of funny to me.
Skylanders appears to be a rather good 3D platformer on the 3DS. It might not be for everyone because of the toys you use, but for the people who play this game - both young and old - it might be an awesome experience when it hits stores this October.