When you think of ‘Creeps’ in a tower defense game, most tend to think of expendable yet loathesome blobs of stats, just waiting to be chipped away at by your mathematically positioned defenses. In the Creeper World games, you’re up against something much more elemental. Something more organic, and much bigger. You’re fighting an ocean. An ocean that hates you.

Despite being squarely based around the idea of fighting a rising tide of fluidic death, Creeper World 1 & 2 (by one-man indie outfit Knuckle Cracker, and developed for both PC and Mac, nicely) take two very divergent approaches to the concept. First up to bat is the original Creeper World. Taking a top-down perspective on things, the threadbare story of the game revolves around a grand exodus across the universe. Your task is the evacuation and defense of Odin City, the last (and thankfully mobile) human city, currently on the run from the Creeper, a seemingly unstoppable blue, gelatinous, corrosive wave that is consuming planet after planet.

If you’ve ever played bizarre Russian RTS game Perimeter, you’ll feel right at home. The inspiration is clear, although Creeper World is a much more low-fi experience, with each level playing out on a single-screen map. Each mission begins with your city being plonked unceremoniously somewhere on a planet that is about to be consumed, and your goal is to place a spiderweb network of resource-gathering relay towers (which only function when linked in some fashion to your base), then establish defenses to first hold off the creep, then build up enough firepower to push it back long enough to grab several objective points, opening the warp-gate to yet another doomed planet. And then you do it again and again until you’ve found a planet that isn’t trying to eat you.

While very high-pressure and tactically demanding (especially if you’re trying to shoot for an efficient high score) Creeper World is very simple and intuitive. Aside from the later wrinkle of random creeper-bombs that directly launch blobs of the all-consuming goo inland, the creeper is a predictable elemental force. Spawning infinitely from a few points on each map, it rises as it builds up, flows as you’d expect, and spreads when given a chance to expand into lower terrain. You gain most of your defensive weapon types quite early in the game, and most of the gameplay variety comes from the creative layouts of each map. You need to really put some thought into where you position your guns, as terrain elevation and depth of surrounding creeper can greatly effect the usefulness of a weapon.

Sometimes you’ll be trying to set up defenses before a levee wall breaks under pressure and you’ve got a fifty foot tsunami of death to deal with. Other times, the creeper will be comparatively easy to manage, but you need to rush to rescue survivors from around the map before they’re dissolved. In one notable early mission, you have an initially simple setup – a wide open area to expand around a volcanic caldera, but there are a multitude of creep spawners at the bottom of the crater, generating it at an enormous rate. Before long, it’ll overflow and drown everything around it in one massive blue gooey eruption, so you need to get to the lip of the caldera as quickly as you can and start chipping away at it before you’re overwhelmed.

The main strategic concern in the game is your resource network. Much like your city, your turrets can relocate freely once built but they can’t operate without power once they’ve landed, so you need to place them close to your expanding resource-gathering/power-distributing network. Of course, the network itself is defenseless, and a single blob of creeper in the wrong place can shatter the entire chain and leave a whole wing of your defensive force cut off without ammo, so you need to continually expand and defend at the same time. While it’s possible to win most levels through slow and steady attrition, gradually building up resources and pushing the creeper back, the key to high scores is being fast and decisive, expanding with mechanical precision and ensuring that the flood never spreads too far.

There’s a remarkable amount of depth to the game despite the initial gameplay mechanics being simple and quickly introduced. And for those wanting a variety of challenges and high-scores to beat, there’s a whole boatload of user-made and bonus stages outside of the main campaign, and even a random map generator to top it all off. It’s a solid and clever game, and worth a look, but perhaps a little limited to really last long-term, due to it introducing most threats and core game elements quickly, and only giving you small variations on them as the campaign goes on. But that’s only half the story here – Creeper World 2: Redemption takes those concepts and moves them off in a very different direction.

For the sequel, the game shifts to a side-on perspective, with a focus on that most popular of indie tropes; mining through blocky environments. Still, this is unmistakably a sequel to Creeper World, and the core game-flow remains largely the same, although given a more offensive spin. While the first game had you constantly on the run from the creeper, the sequel is about the fight to reclaim the galaxy from it. From your mobile reclaimation ship, you cut tunnels into the earth, build defensive and resource-gathering units and construct weapons to fight back. This time you don’t need a connected network of power nodes to make things happen (although you do need command pylons to increase your building/command range), and so long as you’ve got a clear path between you and the thing needing power or ammo, it’ll get there safely. Later on you can even place teleportation nodes to speed up your logistical efforts further, cutting the travel time of each power or ammo packet down to moments.

The talking heads of the story mode tell you that science has finally given you the means to destroy creeper spawners once and for all, but in order to do so, you need to push the wave of corrosion all the way back to the point of origin to give yourself enough time and space to deploy a spawner-destroying bomb. Gone are the worries of height and depth, and are replaced with other physical concerns; pressure and gravity. Many of the levels have gravity that pulls in an unusual direction, or with uncommon weakness or strength. On top of that, some levels have gravitic anomalies, pulling normally flowing creeper into densely packed defensive walls or pinpoint concentrations that will eventually reach critical mass and flood the entire level.

Your weapons to use against the creeper are largely taken from the first game, although a few new tools join the game, including the rather clever repulsor ray, which (at varying costs of power) extends a beam of variable length that pushes creeper back without destroying anything, allowing you to reclaim tunnel segments and move units into position safely. There’s a few new threats to worry about too, though, including kamikaze drones usually spawned from gateways deep inside creeper pools. They’ll make their way in increasing numbers (most levels are easily lost if you don’t push hard enough to stop enemy growth) towards your nearest installation and try to explode it, meaning that you can’t just win with passive defenses. Guns always need to be put on the front lines to cope with mobile threats.

The mining element of the game introduces a lot of strategic depth, too. It costs energy to chip away at the earth, and some weak rocks can be eventually dissolved by creeper, giving you a time limit of sorts. On some missions, the enemy will directly mine out areas over time, too, although you can see in advance what areas will be destroyed so you can prepare. In the depths you’ll find resource gems and minerals to mine. The minerals are especially important, as they fuel your greatest, most flexible weapon; anti-creeper. You can create your own mobile creeper generators which continually pump out benign white creeper. Harmless to all your units (and presumably the environment at large), but it neutralizes an equal mass of enemy creeper on contact. As most missions begin with you at the top of the map, and the blue goo rising from below, it’s often a safe tactic to passively flood the lower tunnels with your own creeper to set up a defensive buffer of sorts while you prepare for a more decisive strike.

There’s a lot to think about, and it’s mostly intuitive stuff, dealing with familar concepts like the flow of liquid and building pressure in various parts of the tunnel network. The growing number of enemy threats, including counter-mining, suicide drones, gravity warps and more help keep the missions fresh to the end of the campaign, wheras the limited elements of the original perhaps started to wear a little thin by the time you reached the final missions. There’s a lot of meat on these bones, and levels are far more varied in scale, too, with the maps scrolling deeper and deeper down, and some levels even forcing you to fight your way up from the depths, rather than digging your way down.

As with the first game, there’s a fairly sizeable story-campaign to slog through, and a bundle of bonus missions on top of that. While the first build of Creeper World 2 seemed bare-bones compared to the original, a random level generator and level editor have been included in the latest build, and there seems to be plans for further expansion and tuning as mentioned on the developers blog. My only real complaint with the core gameplay in Creeper World 2 is that the final cleanup phase of each level can drag on a bit. Many missions require you to clear out every last bit of enemy creeper, which means carefully scouring the map and eliminating each little puddle – whether harmless and contained or not – with a manual strike.

As you can see from the screenshots and trailers above, neither Creeper World game is particularly pretty. Or really pretty at all. Developed in Flash, they’re almost the definition of ‘programmer art’. Simple shaded geometric shapes and clear representations of game concepts. The visuals are designed with readability in mind, letting you see relative heights and depths on a 2D overhead/side view, rather than giving you anything to marvel over. On the plus side, these games will run on pretty much any computer you can throw it at (including a laptop with an ancient integrated graphics chip – tried and tested), but the graphics are probably the weakest element overall. The music is a decent mixture of fairly memorable and tense tunes, but you’ll probably tire of them before too long – there’s not nearly enough tracks to last each game in its entirety, and it sounds a little overly compressed to keep game file-size low.

Still, quibbles in presentation aside, there’s only very minor gripes to be found in the core experience of either game. While the tower defense genre may be getting a little played out lately, the Creeper World games put a very fresh spin on the concept, and offer a large number of well designed missions, as well as an infinite number of randomly generated stages. There’s a lot of content here, and while the presentation is simplistic, there’s nothing here to obscure the information you need to see, or get between you and the orders you need to give to your defensive line. While each of the Creeper World games is sold separately for $10, you can buy them as a double-pack for $15, effectively bringing the simpler first game down to a quite reasonable $5. If you like TD games, or just solo strategy in general, there’s a lot to like here.

But don’t just take my word for it. There are fairly hefty demos of both games available on the official site, even offering levels that don’t appear in the full game, and providing a standalone, extended tutorial of sorts. Even if this review has convinced you, it’s well worth trying them out for yourself before putting down any money. Either way, give these games a shot. They’re inventive and unique, and that’s good enough for me.