The Nikoli puzzle factory is filled with evil geniuses. There really is no way else to explain their signature puzzle types sudoku, kakuro, hitori and the plethora of others that have hit the eShop by way of developer Hamster — the puzzles are simple in premise, seem easy enough to complete but then dropkick your brain when you've come too far to turn back.

Nurikabe by Nikoli is possibly the most devious puzzle type yet, draped with ease and filled with tormenting challenge. Much like Hitori, Nurikabe begins with a white grid riddled with numbered cells and asks players to paint in black cells while obeying its rules: Only blank cells can be painted, and they must connect on at least one side and eventually form one large group; the numbers interspersed — called "islands" — dictate the total of white cells in its island; islands may not contain more than one number cell or no number cells at all, so no strays or double-ups; and the most jerk rule of all, painted cells cannot form squares larger than 2x2, meaning no Tetris-style cubes are allowed anywhere.

It sounds a little complicated and, well, that's because it is — Nurikabe is not for beginners. The helpful tutorial walks you through the steps involved in solving a simple 7x7 grid, and, while the rule set is a little overwhelming at first, by the end it doesn't seem so difficult. But no puzzle grids are that small in practice — they're a terrifying 18x10 to start with, and only five of the 50 puzzles on offer are classified as "easy."

Without a proper hint feature, you're left with only your wits to get you through, and if this isn't the kind of puzzle you connect with then it can take a mental marathon to get to the end of a puzzle that, by the end of it, doesn't necessarily make you feel all that clever. Persistence is critical — over time your brain makes note of shortcuts that help clip things along, but only after staring at and twisting around puzzles for a while. Whether you get there or not depends on your tolerance for being wrong for long stretches.

The steep challenge is by no means a slight against Nurikabe — even if it can seem overzealous at the outset — and in fact makes it a very good choice for experienced puzzle mavens. Because of their challenge, the 50 puzzles on offer will certainly take a while to get through, providing seemingly more bang for your buck than other Nikoli offerings.

Unsurprisingly, Hamster hasn't changed up the feature set or interface for Nurikabe, so there is still no hint system to get bailed out of a brain-dead moment — which is especially unhelpful. And as the grids get larger the cells can appear incredibly small on the touchscreen, which the top-screen magnifying lens is absolutely no help in alleviating as it zooms in far too close to be of any reasonable use.