Additionally, the more powerful cards normally can't be used until at least four creatures are in play, which opens the "Summon Lock" and lifts all restrictions on what you can whistle up. You'll also need to be mindful of what element the cards are tied to (Earth, Water, Wood, Fire or Biolith), because if you place them on a space that doesn't correspond - like, say, putting a Water creature on a Fire space - your creature will either show up weakened, or be instantly killed.
Battle Arena games can be played against the computer, with a friend (you'll both need your own decks, naturally) or online. When playing without an online connection, you'll be free to draw whatever cards you want; that is, you can play any of the cards in your pre-established, customizable deck of 30. (That's in addition to the four reusable "action" cards, which enable you to do things like telling one of your monsters to attack, get a monster's stats or end your turn by putting a card in front of the camera.) The starter pack is automatically registered with the game, but if you want to create your own - say, with cards that you bought separately - you'll need to "register" them by showing them to the Eye (which can only read four cards at a time) and then sort them into a custom deck, which is a lot less tedious than it sounds.
You'll also need to do this before you play online (whether you're playing with the Starters or not), and online play comes with an additional restriction: to keep you honest, the computer will tell you which cards you can draw from the stack (up to five can be in your hand at any given time). This, for lack of a better word, is a pain - especially if you run out of summon cards and keep being dealt semi-useless spell cards - but it'll usually keep your opponent from playing exactly the card he/she needs to completely cancel out your last move, which the computer does with irritating frequency.
For all its apparent complexities, the Battle Arena game is fun and easy to get into, and you can customize your matches to leave out the sometimes-lengthy battle animations, or put a time limit on each player's turns. Matches don't usually last too long (although if you get a skilled opponent with a good deck, you can get a lengthy, tense war of attrition going), but it's fun, and the additional cards promise to give an unusually long lifespan to what's essentially a tech demo.