Aside from downloadable content that lets you dress a marshmallow in a medieval helmet, Rise of the Blobs (Free) doesn’t have much in common with Wind-Up Knight. Both are made by Robot Invader, but Wind-Up Knight (Free) was a viciously funny precision platformer while Rise of the Blobs is a matching game with broader humor. Jiggly blobs, fruit splatters and big bright colors, all these things are hallmarks of a friendlier, simpler game. Here’s the thing about Robot Invader’s games, though—what you can see on the surface rarely reflects the depth of what’s beneath.

Let’s not give too much thought to the premise. A friendly marshmallow named Mal stands atop a mighty, rotating tower while cubic blobs rise up below him. He throws down fruit of many colors at an increasingly frantic rate. If you match a piece of fruit with the same colored blob it will be absorbed, and you can pop the whole works. This triggers a chain that pops any adjacent blobs of the same color.

For a few seconds, Rise of the Blobs might fool you. It might make you think it’s a walk in the park. Not for long. The difficulty curve is steep. The first few lobs of fruit are slow and steady, and the swipe-to-drop mechanic comes in handy.

Then things get faster. And faster. And even faster. It isn’t long before it takes herculean effort just to get the tower into any useful position before a given fruit lands.

This isn’t a match-three, it’s a match-one. Ideally, you want to match one fruit to one mass of blobs —anything else is wasteful. Sometimes you might pile up an extra piece of fruit or two to connect blobs into a bigger chain, but matching three fruit is something you only do when you need to clean up a mistake.

The other path to dealing with mistakes, or giving yourself a slight breather when things get overwhelming, is to use one of the power-ups that are unlocked as you go. This is the sound of the other shoe dropping: you can buy power-ups with coins that you earn while you play, or with coins that you buy as you go. Better, perhaps, to compete with the folks on your Facebook leaderboard than against the potentially spendy masses in Game Center. There’s no ‘pay to win’ button and the cooldowns are hefty, but deep enough pockets can earn themselves a reasonable advantage.

That said, Rise of the Blobs has me much more interested in testing my skills against myself than with the entire rest of the world. The game has a modified take on the mission system every arcade game comes equipped with these days. You have three missions to deal with at a time – things like popping a certain number of yellow blobs, or reaching a new score in a particular mode. They aren’t replaced until you complete all three; when you do, you get a random reward—a pile of power-ups, a new outfit for Mal, or a big boost of XP. Earn enough XP and you rank up, unlocking new stages, new modes and more bonuses.

These alternate methods of progression haven’t kept me in power-ups to the extent that I’d like, but them plus my coin income has been just about perfect. Everything extra goes into leveling perks and upgrading power-ups. It’s not the particular reward that keeps me going, though. It’s the mystery. If I complete three missions, what will I get? Could it be a new outfit (and they are so very cute and often clever), or will it get me my next rank? And what will I unlock then?

The missions also do a great job of leading you through all the different game modes. There’s Skull mode, where you have to reach and clear skulls before they count down to zero. There’s Timed mode, in which you collect clocks or die. And there’s Match mode, which requests certain patterns and rewards you well for popping blobs in the right order.

None of the modes does anything drastic to the game’s formula, but they all do a great job of making it significantly more complicated. It’s a funny thing—the steep difficulty curve can be extremely frustrating, but at the same time it’s what keeps me coming back. I know if I can just break past the point where my mind and fingers give up that I will be able to reach much greater heights. I can almost taste it. There’s something to be said of demanding skill and practice—these plateaus are a great motivator.

Rise of the Blobs isn’t the follow-up to Wind-Up Knight I hoped for. Taken on its own, however, it’s quite the catchy matching game. It has little to do with Tetris beyond blocks falling from the sky, but it evokes something similar. It’s that feeling of noticeable improvement, of being able to push further and make the game continue longer each time you play. Unlike Tetris, however, you don’t need to sit for an hour to get there.

In a sea of matching games, few feel simultaneously as rewarding and as respectful of a player’s skill as Rise of the Blobs. It may be soft and jiggly on the outside, but it’s hard as nails underneath.