It's apparent that the PlayStation 4's 2015 gaming year will most notably be remembered for a handful of exemplary AAA open world games, but pulsating under the radar there has also been a fine array of pixel art 2D games released on the console this year. With examples like Shovel Knight and Super Time Force Ultra, this is partially the result of the cream of 2014's pixelated crop being ported and updated from other consoles. Games like Shantae: Risky's Revenge - Director's Cut stretch even further back – alternatively La-Mulana Ex is an instance of this on the PlayStation Vita – but regardless of the late arrival of these titles, they are still welcome additions to a retro inspired library. First released on the Nintendo 3DS and Steam in late 2014, Xeodrifter fits well within this list, and it can sit proudly beside its sprite-ly 2D peers.

Xeodrifter is a side-scrolling action adventure game, which originated from developer Renegade Kid's idea to create a 2D demake of their 3DS sci-fi first-person shooter property, Moon Chronicles. Jools Watsham, the co-founder of Renegade Kid – who was also responsible for the design and art in Xeodrifter – approached it as a passion project based upon his appreciation of the Metroidvania sub-genre. In this sense, apart from the basic story opening of a spaceship crashing into an asteroid and skidding out of control resulting in a broken warp status, the player composes their own narrative from their approach to exploring four nearby planets. The main goal may be to collect a green crystal to fix your ship's warp core, but this is an understated backdrop to establish drifting between locations, and wandering around the alien environments.

From the outset the staples of trusted Metroidvania design are apparent as you methodically analyses initial dangers to find pathways around each planet. Even a simple water basin must be tested to ensure that it can be touched and navigated through, as sometimes a planet's liquid will be bubbling in an unapproachable manner. It doesn't take long to discover that defeating a boss is essential for progress, since they each drop a power-up that eventually unlocks six new skills, and every fresh ability opens a blocked route. This in turn introduces the opportunity to loop back around, and access unmapped sections of levels.

While a couple of power-ups are predictable by serving to provide the equivalent of a key to bypass a locked doorway, at least half of Xeodrifter's upgrades have an interesting consequence upon the gameplay by changing how the player searches for potential paths. With experience of designing stereoscopic 3D games to include an extra background layer in games like Mutant Mudds on the 3DS, Renegade Kid is clever in Xeodrifter through the Plane Shift Power, as it doubles a planet's area to explore by adding a second depth of field. Similarly, the Rocket Power reveals potential shortcuts, and alters how you interact with the environment's verticality, especially in regard to seeking out collectibles strewn across hidden areas of the four maps.

The game benefits from presenting a fast pace to its run-and-gun mechanics, where you can hold an autofire button to shoot upwards or the way you're facing, and also duck or jump to fire at lower enemies. Therefore, shooting is more versatile than a Mega Man game, but not quite as flexible as the diagonal fire in a Contra title, depending upon your weapon improvements. There are no unnecessary fetch quest trinkets in Xeodrifter; every concealed health meter or gun extender makes you stronger, and the gun upgrades can be equipped on a sub-screen to diversify the focus of your firepower. It feels satisfying to switch between your preferred gun arrangements, as you choose between a spread shot and a wave gun, or the possibility of increasing the rapid fire, alongside the intensified power of bigger bullets.

In an astute approach to Metroidvania design by Renegade Kid, the ferocity of enemies is a clear visual indicator of the difficulty level of a planet. Consequently, you may decide that you're not yet ready to investigate beyond a huge square rock creature, which blasts a laser beam from its eye that consumes half of the screen, or an alien bat that swoops down to fixate on you. However, there is a sense of disappointment in that the seven main bosses are merely altered colour variations of the same beast. Despite this, the way each boss adds new attack patterns, and movement arrangements to escalate their core assault ensures that you face a shrewd new iteration in each battle.

Xeodrifter's art design is not intended to be as detailed as more recent 12-bit styled graphics, which present a hybrid middle-ground look between two classic eras, although its bright colouring is themed from an NES palette. The deliberately simplified presentation is clear and coherent, with pleasant touches to effects like the sprites rippling underwater, or the way defeated enemies burst into pixelated pyrotechnics. The animation matches the speedy pace required for long floaty jumps, and it suits each scene, so while standing still during quiet contemplation, the small main character bobs contently. It's also subtle in the way an external planet's colour can distinguish the depiction of internal environments, with dusky blue backgrounds and red bubbled corridors corresponding with their relevant planets' colours on the star chart.

The music is also used efficiently to differentiate each location. Considering that Jools Watsham recognises Super Metroid as a milestone in gaming, the importance of a soundtrack in establishing a Metroidvania game's atmosphere must have been apparent to Renegade Kid. Even within a small team, three contributors were integrated to enrich the game's soundtrack. Matthew Gambrell's warbling bleeps and fizzling sounds during the Xeodrifter title screen track establish the mood for visiting an alien galaxy, and Roth Sothy's chiptunes complement this tone effectively throughout the game. The Starchart music for the map screen balances this with an uplifting tune that celebrates space exploration, as you decide which planet your ship should visit next, while the tempo of the Native Life-Form track ramps up the tension for each boss battle. Finally, these cohesive sounds are brought together after you complete the game as Brian Altano's well pitched As The World Falls Down (Redux) synthesized tune plays over the end credits, leaving the player to reflect on their journey.

Since the adventure is designed to encourage exploration and discovery, as opposed to holding the player's hand, Xeodrifter is most challenging during the opening sections of the game. Starting with low health, as well as an underpowered gun, it's advisable to tread carefully and patiently at the outset to avoid the dreaded 'life system fail' message. There are checkpoints just before meeting a boss, or you can save back at your spaceship, but if you die without saving after drifting deep into the core of a location, all of your map progress and collectibles will be lost. Backtracking is a necessity in a Metroidvania game, and although Xeodrifter could benefit from including more mid-level checkpoints, the actual size of each of the four maps is approachable due to their small scale, plus power-ups unearth some basic shortcuts.

Once you acclimatise to the flow of the game, and learn to be thorough in checking every possible empty area of the map for a hidey-hole or a concealed walkway, the multitude of health and gun extenders becomes empowering, and flips the difficulty balance. It's feasible that you'll beat the game in less than four hours – alongside achieving the Parametric, Security Blanket, and Explorer trophies for visiting 100 per cent of the map, and finding all the collectibles. Due to the familiarity of the attack patterns, and a smorgasbord of upgrades, the game's final boss is also easy to defeat, so it's worth battling for the Snoozefest trophy by destroying the end-game beast without taking any damage. Similarly, the Speedrun trophy for completing Xeodrifter in less than one hour feels like a fresh challenge, and a neat way to harness your newfound knowledge of the optimum routes to tame previously hostile levels.

This game's structure has been intentionally designed to be compact, simplified, and cleverly arranged to produce a sharpened Metroidvania experience during a delay in the development of Renegade Kid's larger Treasurenauts project. In regard to Xeodrifter's five month development time, Jools Watsham explained to Push Square's colleagues at Nintendo Life that "It was a real shotgun project in terms of focus, speed, and effort. It was definitely a labour of love". Therefore, Xeodrifter may not be as large, or sprawling as a game like Axiom Verge, plus it doesn't quite have the imagination to its characters and prominent level design of a linear platforming title like Shovel Knight, but at £6.49 it also only costs half the price of many of its pixelated peers. With the inclusion of cross-buy for PlayStation 4 and the PlayStation Vita – although it doesn't incorporate cross-save – a few hours spent gravitating towards Xeodrifter may just be the quick palate cleansing variety a gamer needs after spending months with one of 2015's distinguished open world, big budget titles.

Conclusion

Xeodrifter is Renegade Kid's concentrated approach to a Metroidvania game, where you drift between four tightly designed planet maps to explore undiscovered alien landscapes. Encountering seven iterations of the same boss as you wander – albeit each with fresh attack patterns – unlocks six power-ups, with the more imaginative skills uniquely altering progression through the levels. Small scale maps, plus a four hour game length ramble, may seem like an introduction to the genre, but a reverse difficulty curve that negates hand-holding ensures that Xeodrifter is harder at the start, and easier at the end when you're fully powered-up. A five month development cycle has resulted in a focussed and succinct sci-fi action adventure, which sets a fast pace to flow through its bright pixel art presentation, and waft along to its atmospheric chiptunes.