Opening TitleDouble Battles in the Wild (Yep, now you can simultaneously fight 2 wild Pokemon in certain areas of the game)
VS Trainer: Triple Battle (Takes a little getting used to, but now you can simultaneously fight three Pokemon at once. More on this below)
The following videos may contain spoilers:Zekrom EntersReshiram EntersI wasn't sure if the legendary Pokemon's entrance cutscenes were spoilers or not since they contain no dialogue but I'd advise you not to watch them if you like discovering the game's storyline yourself first-hand. Also, they are in full 3D and look really awesome.
As promised, here's the mechanism for Triple Battles explained:1. Normal Triple BattleYour opponent sends out three Pokemon and so do you. Whenever a Pokemon attacks, it can only attack either the Pokmon directly in front of it, or any Pokemon adjacent to it. For example...
A B C (Opponent's Pokemon)
D E F (Your Pokemon)
Pokemon D can only attack Pokemon A or B
Pokemon E can attack Pokemon A, B, or C
Pokemon F can only attack Pokemon B or C
You can switch your Pokemon's positions, but that will take up one turn for that Pokemon.
2. Rotation Triple BattleAgain, you opponent sends out three Pokemon and you follow suit. This time, only one Pokemon is active on both sides. This Pokemon can only attack the other side's active Pokemon.
During your turn, you can choose to attack normally, or to rotate. When you choose to rotate, the Pokemon will not rotate just yet, as you will be allowed to choose an attack for that Pokemon too. Once that is done, your Pokemon will rotate and attack in the same turn. Rotations always occur before any attacks, so this gives a slight difference to just switching out your Pokemon.
(The clip I recorded was a standard triple battle, not a rotation triple battle)
Also, triple battles are quite rare. I've just completed the Elite Four and have so far only encountered one rotation triple battle that was compulsory. I'm sure there are a lot more to find elsewhere...
Note about wild double battles:When you fight two Pokemon in the wild, you can only capture one. Pokeballs can only be used after one of them has fainted.
Other Random Notes:-TMs are now infinite use
-Some normal trainers can use Full Restores
-Some bosses have up to three Full Restores
-Pokemon Centers have undergone a merger with PokeMarts
-You can now trade or battle without having to run all the way to the nearest Pokemon Center's Union Room
-Pokemon Black and White each get their own exclusive area on the map
-You cannot trade Pokemon with fourth generation carts or below, but you can transfer Pokemon from fourth generation carts onto Black or White in a one-way process
-Pokemon contests have been replaced by musical shows
-You cannot encounter any Pokemon from previous generations until after the Elite Four
-The first Pokemon in your party no longer follows you around like in Heart Gold or Soul Silver