Skylanders: Trap Team's adventure has you helping Eon in the Eternal Archives. It seems one of his helpers has read the wrong book and accidentally cast a spell on Skylands. Now everybody is falling asleep and their nightmares are coming out into the real world. Eon has called upon you and your Skylanders to help wake everyone up and end the spell.
The Eternal Archives is broken up into five sections, and each of the levels ends in a boss fight that, when won, puts a new trapped villain in your collection. You will not need the Trap Crystals used in the console versions in order to capture these enemies. Instead, you just need to perform the necessary swirling motion on the touch screen and the captured enemy falls into the lower screen of the 3DS, ready to be called upon to perform its attack.
The use of the trapped villains is actually another difference between this version of the game and the others. Where the consoles swap your Skylander out for the converted villain, when you summon your defeated foe in this game, they appear and perform some kind of devastating attack. Afterwards, they return to their crystal (the 3DS' lower screen) and a counter starts denoting their cool-down time.
Like Skylanders: Swap Force, you aren't relegated to a select few Skylanders. Once again, you can load up as many characters as you like (provided you have the patience to keep the portal synced with the 3DS). This, of course, means that you aren't relegated to the Trap Team characters as the game easily accepts all previous toys, but you do get a bit of a bonus if you use the Trap Masters. If you are fighting with one of the new big characters, then an extra bar appears on the HUD. This one slowly fills as you collect enemy drops that look like trap crystals. Once full, you can activate a powerful attack that will damage, if not destroy, all of the enemies on the screen. Between this attack and the ability to call upon trapped villains, you will have quite a few options when taking on some of the game's bosses, though you will probably not really find a use for these powerful attacks while running through the rest of the level, but more on that later.
Skylanders: Trap Team also brings back the Skystones mini-game. Like before, this tile-game has you and an opponent battle for control over a board. When you place a tile down, the number of teeth on each side of the tile is compared to the number of teeth on an adjacent tile, and if you have more, the enemy tile flips to your color. While there are plenty of times when you have to play this game in order to progress the story, a new feature with Trap Team is the ability to look for opponents online.