Three aquatic characters from the Bubbly Primes math game.

Fun Characters are Key

In order to be enjoyable, a true educational game can’t just be a thinly disguised quiz or test. It needs to have visual appeal, although by itself, that’s not enough. It also needs strategic elements that make it a real game. In Bubbly Primes the critters, and their interactions with the player and the rest of the game, provide a lot of what really makes the game fun and engaging.


Xrympy (pronounced “Shrimpy”) looks like a little crustacean, and is usually the first critter to appear.

Three Xrympy swimming with number bubbles.

She swims slowly across the screen bouncing all the bubbles that she touches. She has a powerful downstroke, so when she bounces a bubble downwards it can often help by giving you more time. Sometimes, however, her presence is not so helpful. For instance sometimes when you are just about to pop a bubble, she gets it first, scattering bubbles in all directions. If you tap on her she temporarily blushes a faint magenta color, swims backwards, and stops using her strong downstroke. After a few seconds, she resumes her normal activity.

Original hand drawn pencil drawings of Xrympy displayed side by side.

Pencil drawings used to create the Xrympy animations

Xrympy was hand drawn with pencil. The frames were then scanned on the SCBI scanner, and processed in GIMP. The white background around her was removed, the pencil lines were darkened until they looked like India Ink, and then she was colorized. Finally the frames were exported to the Bubbly Primes codebase, where the code that makes her swim could bring her to life.


The second character to appear in most games is Yrchy, modeled after a sea urchin, and pronounced “Urchy”. Yrchy is composed of many layers, which were drawn separately and superimposed in software when the critter comes onscreen. The layers are coded to gently expand and contract breathing life into the animation.

Two different size Yrchy with some prime number bubbles.Image of a purple Yrchy.

Yrchys tend to come into the game in waves.

Each of the critters is capable of being either help or hindrance to the players. Beginners tend to find Yrchy more of a hindrance. Her prickly spines pop every bubble that she touches, which causes composite numbers to factor and prime numbers to pop lowering the player’s score (From an educational perspective, the game “knows” that the player didn’t get a number right or wrong when Yrchy is responsible for touching it.) When Yrchy is tapped, she temporarily turns purple, and in this state, she doesn’t pop bubbles that she touches.

Advanced players have sometimes been seen intentionally nudging Yrchy towards areas thick with rising composite numbers to pop them faster than a person can; even if she gets a few prime numbers, it can help simplify the screen at times when the number of bubbles starts to feel overwhelming.

Pepper the Fish

Pepper the Fish is a very interesting character. Her animation is the most complex and sophisticated of the critters in the game so far. Her components are each frame based pencil drawings, like Xrympy. However, those frame-based parts are composited together in real time using techniques similar to those with which Yrchy is constructed.

Two Pepper the Fish characters swimming in the same direction.

Sometimes Pepper will swim fast to catch an Yrchy or a particularly big prime number.

When Pepper the Fish swims through the game, she scatters bubbles in all directions. In that sense, she is like Xrympy but more troublesome. Although her stroke is not as powerful as Xrympy, she sends bubbles both up, down, and in all directions. Although she usually swims slowly, at times she will pick out an Yrchy to eat! (Bubbly Primes was made in Southern California where there is a sea urchin harvest.) Occasionally, she might select the largest prime number to pop instead. When she selects a target in this way, she will pick up the pace, sometimes making elaborate U-turns. If she succeeds in catching her Yrchy, or popping the large prime number, she will then swim out of the game. If her target is removed from the screen first, she will resume her slow meandering. When she is tapped she temporarily blushes a greenish color, forgets about the Yrchy or large prime that she was honing in on, and goes back to her slow circling of the screen.

You may have to play the game for a while to get a high enough score to catch a glimpse of Pepper.

Adding depth to the game

The reason the critters are not straightforward opponents is to add depth to the game and make it more interesting. Although initially, players may feel the critters to be adversaries, they are designed so that a player who knows them a little better can interact with them in interesting and fun ways.

You’re always welcome to email us with questions about the game or its critters. We love hearing from fans of the game! You can also leave comments on this page asking questions about the critters or suggesting clever ways to play with them in Bubbly Primes (if you post, please be patient, because the comments are moderated to avoid spam).

We have some great ideas for additional critters in future versions of Bubbly Primes. We can’t wait to code them up and release them!

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