You know that old saying about cats having nine lives? Well, as far as Mewgenics is concerned, you can forget it – and you can also forget the idea that a game about cats has to be in any way cute. These kitties are red in tooth and claw, prone to strange mutations, and strictly limited to just the one life, which often ends swiftly and brutally.

Such is the nature of roguelike, a format that has spawned some of the biggest indie hits of the past 20 years. In these games, failure is permanent; dying sends you back not to the last checkpoint but back to the beginning, the game reshuffling its elements into a new shape for your next run. And so it goes in Mewgenics. You gather a party of four felines and send them out on a questing journey, from which they return victorious or not at all.

Down in the sewers, Joyce, the tabby mage, gets trampled to death by a blob-monster. Shortly afterwards, Fulbert, with his Bagpuss-like markings and full beard, is exploded from within by maggots that have infested his guts. That’s the last you’ll ever see of either of them. But the pair enjoyed one magical evening together before shipping off to war, leaving behind a kitten with that telltale pink-and-white patterning (and some promising stats), ready for the next go-around.

These emergent family sagas are told in the second of Mewgenics’ two modes: a pet sim – think Tamagotchi meets Love Island – where you furnish your cutaway-diagram home and grab cats by the scruff to drag them between rooms. As well as matchmaking partners who may produce the next generation of warriors, you’re trying to separate love rivals – whose scraps are yet another way these cats can meet their end – and members of the same family.

If you find the title’s pun distasteful, be warned that it’s an accurate indication of the profoundly tasteless humour that awaits within. Expect an awful lot of poop, undeveloped foetuses and pussy-related single entendres, as well as sections where you watch cats in flagrante (the humping animation can, at least, be turned off). The game’s real shock value, though, is subtler and sharper: it’s in how quickly you grow accustomed to checking the litter from last night’s romantic encounters, then dumping any kittens with subpar stats or inbred birth defects.

The game’s developers, Edmund McMillen and Tyler Glaiel, came up through the early 00s Flash game scene, the heyday of Newgrounds and Happy Tree Friends, and never really grew out of it. Coming to their work, you have to be willing to accept the post-South Park teenage edgelord aesthetic as part of the package.

All that may put you off Mewgenics, and fair enough. But beneath its icky surface you’ll find a game of rare depth and variety. The pet sim is a sideshow, really, to the turn-based battles, which play out like a mashup of chess, D&D and Pokémon. You move your cats around a 10×10 board, looking for ways to leverage the particular combination of abilities and obstacles in front of you. Say you’ve got one cat with a lightning attack, another with a hosepipe, and a third who likes to be electrocuted. With careful positioning, and a basic understanding of water’s conductive properties, in a single turn you can zap multiple enemies and charge up your electrophilic moggy for the next turn.

These eureka moments are frequent, because Mewgenics is constantly throwing new things at you: locations, enemies, classes, abilities, weather conditions, one-off events. McMillen’s previous game, The Binding Of Isaac, launched in 2011 – one of the forerunners of the modern roguelike sensation – and is still being updated and expanded today. At launch, Mewgenics feels as if it has already benefited from years’ worth of tinkering.

What’s impressive is not just the quantity of content but how elegantly it all interlocks. I’ve recently unlocked two new classes, the nature-loving druid and the meat hook-slinging butcher. An unlikely partnership, perhaps, but experimenting yields a discovery: a synergy between the former’s ability to talk to other creatures and the latter’s ability to spawn flies from the rotten meat they carve off their enemies. For the rest of the run, my cats can sit back and let their insectoid-plague army do all the hard work.

These stars may align on your 100th run, or your 1,000th, or never. According to the save screen, after 60 hours, I’ve seen less than a third of what this game has to offer. Mewgenics is built to fill every moment you’re willing to give it.