It's the one game that would be guaranteed to keep gamers hooked on their iPhones and iPads - Pokémon. Nintendo unfortunately, perhaps to keep people buying its devices, is unwilling to let go of what happens to be one of the most enduring game franchises of all time.
There's some hope yet now that the official Pokémon trading card game is now availble on iOS. Sure, it's not quite the same as actually being able to do real Pokémon battles and amassing your horde of murderous but cute monsters but we'll take it for now.
Few games are as cash cows as much as TCGs are. Blizzard currently has a huge success on its hands with the Hearthstone online card game, with characters taken from another popular gaming franchise: Warcraft.
What is appealing about online card games is that you can easily create decks and amass cards without needing to clear space on your shelves. It's also easier to battle with people online rather than having to go to the nearest gameshop to find likeminded gaming opponents.
Not that the Pokémon TCG franchise wants you to stop buying real cards. No, they encourage you to do so and buying booster packs will give you codes to get digital cards or unlock promos. If you've played the card game in real-life, the mechanics are pretty much the same -you procure a starter deck, build it up with boosters and then challenge other players to duels.
Reduce the opponent's Pokémon hit points and you win the game! Of course it's not half as fun as the real thing (though why gamers love the notion of carrying around pocket zoos will forever be a mystery), but if you want your Pokémon and don't want a Nintendo DS, then this is the next best thing.