Back in the early 90s I got sucked into the Magic: the Gathering collectible card game craze. Little Alchemist is a "free to play" mobile version of a collectible card game. And while you can spend real money buying cards (just like I used to do with MtG), it is quite possible to have lots of fun playing without spending a dime.

In the basic battle the goal is to reduce your (computer) opponent's hit points to zero before they do the same to you. Each card has an attack & defense value. You play a card fro your hand of 5 cards which gets matched up with your opponent's card. Any attack value in excess of the opposing defense value does damage to the player's hit points. Played cards are replaced with new cards from your deck and play continues until either player has less than one hit point or runs out of cards.

There are three main battles against computer opponents. "Arena" where you play against other player's decks - earning trophy points & awards, "Adventure" which is a series of battles against unique opponents in a pseudo story mode - earning experience points & awards, and "Portal" which is a special series of battles against a single opponent which get gradually more difficult - earning experience points & awards. There may also be a way to battle against another player directly (true PvP), but I haven't explored this. Awards include in-game coins (used to buy a pack containing a random card), cards, and jewels (usually purchased with real $$).

There are two types of cards: "combo" cards - which may be combined with other "combo" cards to yield a different (hopefully more powerful) card and "final form" cards which cannot be combined. Combining two combo cards also adds to your total combo points. Playing a final form card has no impact on combo points, while playing a combo card on its own will cause your combo points to reset to zero. Before each battle you can set whether your current combo points cause damage to your opponent, add to your hit points, or increase the attack & defense of the card you play. (Special final form card upgrades also have special abilities which consume combo points.)

So unless you spend lots of $$ purchasing high powered final form cards, a big part of Little Alchemist revolves around combo cards - more specifically around the combination themselves. Each combination must be researched separately - so a new combo card is of no real value until you have researched the various combinations. Fortunately, research only takes time - not money; although you are limited to only researching two combinations at a time. There's over 50 combo cards (although ~20 of those are rare) and over 800 combinations.

Even after you have researched the combinations, the big challenge is figuring out what combo and final form cards to put in your deck (minimum 35 cards). I wrote a program which tries to determine the best set of combo cards via brute force exhaustive testing. Unfortunately, this is O(2^n) (where n is the number of different combo cards) and on my i7 iMac the test would take ~24 hours for 35 combo cards; and my wife (who has been playing for several months) has over 40 different combo cards. My current plan is to try to prune down the problem space somehow.

But I'm having fun playing - even if I can't research combinations as fast as I'd like.