changeType/Ditto

There is a grammar to most videogames. A crate, for instance, is almost always there to be opened and looted. These two free games subvert some of the basic rules of videogames to reinvent the "platform" genre.

changeType puts you in a primary-coloured maze that immediately recalls classic Mario titles. But then lets you swap the properties of any two types of objects in the level, as long as you can see them directly to your left or right.

This simple idea means you can immediately turn deadly spikes into safe-to-walk on blocks, but of course, those previously safe-to-walk on blocks are now deadly spikes. changeType encourages you to re-edit the level as you play. Turn the floor into gems for bonus points, but be aware you may fall straight through the bottom of the level; or turn spikes into bouncing springs to reach a previously inaccessible ledge, but you may now be bounced into a previous spring that's now spikes.

For every change, there's a reward and a risk. And as levels progress, the game pushes you to innovate – find new combinations to switch up the level, but your increased skills also lead to intuitive leaps and alternative approaches to puzzles. changeType is ingenious, but also formidably difficult quickly – and unforgiving in its requirement for simultaneous speed, accuracy and thought.

Similarly tough is Nitrome's other new platform game, Ditto. Here, the main character and its shadow/reflection interact in a platform world where your attention is drawn back-and-forth from light to dark. Both the shadow and you can stand on platforms, die from spikes or collect jewels in their respective realms. Ditto's trick, then, is to force you to switch attention between two halves of the screen constantly, often mid-jump. You'll launch off from a platform on the light side (your dark side hanging around in mid-air), to land on a platform on the dark side.

Both titles build from simple ideas, employing charming visuals, excellent mood music and a steady ratchet of difficulty as you progress. Did I mention they're also both free and can be played online in a browser window?

• changeType and Ditto are out now for Mac, PC. Published by Nitrome
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