CDE Humble Gaming was at WWDC 2010 showing of their upcoming trading card game Arena 9. Game developer and long-time Magic: The Gathering player Jeff Lyndon described how they were trying to create an iPhone suitable experience for a collectible card game.
High amongst their priorities was an accessible game that was easy to learn, but also one that didn't overwhelmingly advantage those who had simply collected better cards. The game revolves around a collectible cards that are earned by the user. An initial set is provided, but over time, new cards can be collected by earning in game experience or through in-app purchase. Cards are organized into 5 card decks that you can take into battle.
Battle will primarily be on-line against live opponents. While single-player (offline) mode does exist, it's primarily intended for practice and training as experience points aren't earned.
Battle is waged on a 3x3 grid. Each player's hands is in plain view to the other player, and cards are placed on the grid in alternating turns. The goal is to win as many cards as possible by "turning" opponents cards to your own. The initial rules are simple. If the adjacent number on your the card is higher than the opponent's number when side-by-side, then you turn the other card to your own. Additional rules, however, such as lining up same numbers on two sides or surrounding an opponents card with similar elementals can act as special moves. In addition, the board also has randomly placed elemental-marked tiles that either enhance or detract from a card's power if placed on that space.
Each battle should take about 3-4 minutes and a matchmaking system tries to match you with a comparable opponent. The game is expected to launch during the first week of July and will be free for the base game. Additional cards can be purchased in packs or can simply be earned with enough experience points and wins.