Stealth Inc: A Clone in the Dark was — after a name change from its risqué PC début — a well-received puzzle platformer on various platforms. Its simple but cute aesthetic was matched by some lovely level design, making it a surprise when Stealth Inc 2: A Game of Clones was announced as a Wii U exclusive by Curve Studios, ditching its multi-platform roots. This is a developer that isn't afraid to go with its gut, and what we have on Nintendo's system is a greatly expanded experience, along with GamePad usage that — to a degree — shames the efforts of the biggest studios and even Nintendo itself.

While the original was a set of challenge rooms that were simply selected from a menu, the approach of this sequel is rather the opposite, making knowledge of the last game entirely unnecessary. This time around you play as a specific clone that, right at the start, escapes from a shutdown procedure when it really shouldn't. These clones exist solely to test devious traps and gadgets, it seems, but this little chap's survival becomes a thorn in a weary employee's side. Your foe is a cynical man with a spirit seemingly crushed by working life, obsessing over being the top employee and becoming exasperated by failed efforts to destroy this runaway clone.

While the cut-scenes telling the tale are a bit of a let-down — comprising of slightly dull illustrations and basic animations — the storytelling throughout actual play is terrific. Your foe prods and guides you through the large overworld towards test chambers, manipulating the environment and leaving messages on the walls. There's some deliciously dark humour here, and the sense of being a rat in a maze — but defying your master and actually escaping — is even more satisfying as a result of the setting and overall tone.

Your clone, being short and tubby with colour-coded goggles, has a basic move-set for getting around — you run, jump and hang on ledges, while terminals and switches can be activated and hacked. Early on you're give a gradual introduction to the wider facility and embark on an initial set of relatively gentle Test Chambers, with the designers doing an excellent job of teaching you how to play through simply playing. Only basic controls are provided, but you learn through logic and from making mistakes; a death means an immediate respawn at a recent checkpoint, allowing you to jump right back in. Curve deserves huge credit for pulling off organic learning in Stealth Inc 2, as it feels rewarding and challenging at once; a rare combination, in the current market.

Once early challenges are cleared it doesn't take long for the level of challenge to ramp up. Gadgets become the focal point of each set of Test Chambers — which are in different areas of the overall map — as you work through a number of rooms that use each item in a variety of clever ways. There's an inflatable platform that can also be used to block beams or propel you into higher jumps, while the second gadget is a gizmo to hack enemy robots and units, which are then controlled with the right stick on the GamePad. There are more besides that we don't want to spoil, but we will say that they're used brilliantly in each respective area's puzzles. On many occasions we scratched out head for a good while before being delighted by the eventual outcome, while the later gadgets are a lot of fun to use but deliver fiendish challenges. It's never unfair, but this game is definitely tough.

Level design in the Test Chambers is some of the best puzzle platforming we've seen, with some exemplary moments that show off cheeky humour and sharp instincts from the development team. If they're the highlight, the only downside is the wider overworld; while the Metroidvania concept of exploration and retreading ground with new gadgets is appealing, there are moments of occasional frustration when a wrong turn is taken and fiddly obstacles are tackled again unnecessarily. That quibble aside, the clone facility's various areas are surprisingly diverse in their feel, while the various robotic enemies and drones are nicely designed. There's a large world and a good number of Test Chambers, and as the challenge increases and the gadgets get more innovative it becomes an even more compulsive experience.

In single player this is deliciously balanced, yet Curve has done a truly admirable job with its co-op play, which also makes unique use of the GamePad. Unlocked after the initial set of stages, you can play any unlocked level — or even the main campaign — with another player. While on your own you're forced to use the GamePad, which seems like overkill considering the second screen provides off-TV play or immediately accessible menus or the map. Once you fire up co-op it all makes sense, and this immediately becomes a game to bring together seasoned and less skilled gamers.

The weaker player should probably use the GamePad, and they primarily use the stylus and touch screen and — occasionally — an analogue stick to move specific gadgets. Whereas in single player you place and throw gadgets, sometimes with tricky timing activating their functions, the GamePad player controls items while the other gamer — using a Pro Controller, Classic Controller / Pro or Remote & Nunchuk — moves the clone. It suddenly becomes a game of constant communication as gadgets are used differently, and even hacking terminals requires the TV player to read out numbers for the Pad player to input. Enemies often become 'hidden' and only visible on the GamePad, and pressing and holding with the stylus can reveal these foes or simply highlight an area of interest. The GamePad becomes a box of tricks, with various assist tools also included such as hiding the clone from cameras, making co-ordination and teamwork essential.

This use of the second screen and GamePad is a mix of the Murfy stages in Rayman Legends and some Nintendo concepts in the likes of Nintendo Land and Game & Wario, yet feels like the most cohesive example of the system's capabilities yet. It's the blend of clever stage design and puzzling that finds the magic formula, and is perhaps the best showcase of asynchronous co-op we've seen; we heartily recommend tackling the main campaign in single player, but the option to replay all unlocked Test Chambers with ease makes additional local co-op runs an absolute necessity.

Curve Studios has done excellent work with online integration, too, with automatic online leaderboards after cleared Test Chambers and full-on Miiverse functionality. The star turn is the Level Editor, however — for starters, the Community Levels area allows you to easily search, view, shortlist, play and rate levels designed by other players around the world; the potential for almost endless content is obvious.

Most importantly, the Level Editor tool is fully detailed, and we believe the developer when it says that any Test Chamber from the game can be fully recreated with this tool. You can choose level size and then navigate through 11 categories of environmental structures, enemies, lights, switches and much more that you then position on your blank canvas. Setting and adjusting features can be done fully with physical inputs, with a limited range of optional touch controls; instructions are rather hands-off and there's no tutorial for this tool, but with patience, time and creativity all should be able to create intriguing, memorable Test Chambers for others to take on. Uploading them is also an easy process, making this an outstanding feature.

To finish with presentation, there's a fairly simplistic visual style here that is charming and gets the job done, though isn't necessarily overly attractive. It certainly works, though, and a presentation area that is above average is the soundtrack, which shifts through various styles depending on levels and world areas, but is always a delight.

Conclusion

Stealth Inc 2: A Game of Clones is a gem from Curve Studios, and one of the very best download games on the Wii U. The overworld Metroidvania aspect isn't always on the money, but puzzle Test Chamber design and overall gameplay are of the highest class. On top of that there's a terrific Level Editor tool, a potentially endless source of levels, and co-op GamePad play that provides one of the most compelling demonstrations yet of the merits of asynchronous multiplayer. That latter is important to give some hope to less skilled players, too, as this is also one of the most fiendish titles on Wii U, constantly challenging your reactions and puzzle-solving abilities. If you're up for the challenge, then this is a must-buy on the eShop.