Deck-building games are similar to collectible card games, but you build your deck on the fly as part of the progress of play. And they've proven a gloriously tight fit for translation to mobile.

Ascension was a test case that proved how good tabletop games could be on a touchscreen, with Nightfall and Penny Arcade following in its pioneering wake.

The latest title in the genre to hit mobiles is Star Realms, and it's a little different, and a little more interesting.

While deck-builders might be a natural fit for the medium, Star Realms is the first that's been designed specifically with both physical and digital play in mind.

Card drive

You start out with a deck full of rubbish ships that you can play for trade or combat points. The combat points let you smash directly into your opponent, but trade points can be used to buy new cards from a random selection in the middle of the table.

What you buy goes into your deck, and can eventually be played for more trade or combat points than the starting ships. So your deck gets gradually stronger, until you eventually manage to generate enough combat points to overwhelm your opponent.

This is pretty much how all deck-building games work, but Star Realms does a stellar job of differentiating itself from the pack.

It's unusually vicious. Rather than the tame race for victory points typical of most of its peers, here you're trying to blast your opponent directly.

It's most interesting innovation is the factions. Most cards belong to one of several groups, like the repulsive Blob hive or the terrifying Machine Cult.

Each has a speciality, so Blobs generate fearsome amounts of combat, while the Machine Cult give you more control over your deck. And if you can play more than one card from a faction in a turn, they all generate a useful ally bonus.

Catch cards

There's a catch, of course. You can't predict what you're going to be able to buy, or what's in your hand. That makes Star Realms rather more unpredictable than its peers, and some may lament the slightly shallower strategy that results.

But the increased amount of excitement, and the need to think on your feet rather than falling back on predictable scripted plays, more than compensate.

It's a terrific feeling to peel off and slap down a bunch of allied ships and watch the bonuses snowball.

The other thing Star Realms does well is bases. These are permanent cards that sit next to your play area and offer you some trade or combat points every turn.

That isn't novel in itself, but the game's direct approach to combat means you can either blow away your opponent or attack their bases.

It's tempting to always aim for the killer blow, but leave too many bases on the board and their turn-by-turn bonuses can become game changers.

Space race

Some of the other new things that Star Realms tries are less successful. There's a campaign mode for solo play, but it's really just a bit of meaningless flavour text followed by a standard game against a slightly unusual starter deck.

The designers could have done a lot more to bring this concept to life with some different game modes or a more engaging story.

Thankfully though, the standard two player game is easily enough to justify the purchase price. There's a choice of three AI levels, the hardest of which should keep you on your toes.

There's a serviceable asynchronous play mode as well where you can challenge a friend or get matched against a random opponent.

The game is at its best against other humans. The inherent chaos of the mechanics together with the animal cunning of a flesh and blood opponent can be deliciously exciting.

If you've never played a deck-building card game before, this is a novel and entertaining place to start.