Probability 0

A game by Droqen for PC and Mac, originally released in 2012.
Probability 0 is a game that hides its complexity well. On the surface, it appears to be a simple auto-scrolling game, the likes of which are particularly prolific on mobile devices, with simple controls and no depth. But that is not the case here. The game does auto-scroll through procedurally-generated environments, and the player’s starting movement options are very limited, but tucked behind this simple exterior is a game that offers a great deal of depth, and many reasons to come back and keep playing.

The game introduces its basic controls via an interactive start menu that appears when you first fire up the game, showing that you can move to the left and right, jump, and toss throwing stars downward to break open certain types of blocks. From there, you’re dropped into the menu proper, with options to choose Beginner, Expert, or Karma game modes.

Selecting Beginner immediately drops you into a solid piece of ground with the screen scrolling slowly downward. You need to get moving right away, dropping down to lower platforms as the upper ones are pulled off the top of the screen. Stand still for too long and you’ll be scrolled off the top, which will kill you after a few seconds (an indicator helps you determine where your character is located). Also, falling off the bottom of the screen means instant death.

And so you must move along with the pace of the scrolling. Don’t wait too long, and don’t be too eager. It’s also important to note that you will take fall damage if you drop too far, so you need to consider how close the next block is when planning your descent. While you’re becoming accustomed to the controls, enemies are slowly being scrolled into the area as well.

At first, enemies move slowly to the left and right, with some moving toward your position, and others coming to a complete stop when they reach solid ground. This is good because your only 2 offensive moves are a short-range punch, and downward throwing stars, of which you can only carry a limited supply. You don’t have any way to attack enemies unless they are below you or right beside you. As you descend ever further, more complex enemies appear, including those that explode, others that split into new enemies, projectile-firing types, and even some boss-class enemies that pursue you with noise and chaos.

The goal in the Beginner mode is to destroy as many enemies as possible, and each destroyed enemy will drop an item, such as a health restorative or replenishment to your stock of throwing stars. Items can also be found by destroying certain blocks marked with a star. In the upper right corner, an indicator shows what percentage of items you have collected to open the next “tier”. Opening the first new tier only requires one item, but each new tier requires a few more, making things more difficult as you descend.

Once you have accumulated the requisite number of items, a flashing bar appears across the length of the screen. Crossing the bar puts you into the next tier, restores one unit of life, and turns you temporarily invincible. Temporary invincibility is particularly useful as it negates fall damage, allowing you to drop as far as you like (as long as you don’t fall off the bottom of the screen) when you cross into a new area. Getting hit by an enemy or touching spikes will also make you temporarily invincible, but this also knocks you backward, potentially to your demise at the bottom of the screen.

Crossing from one tier to another also does another very important thing… it opens the upgrade tree, and this is the source of much of the game’s depth. The upgrade tree allows you to change your abilities, which alters the way the game is played and opens up new strategies.

The first time you complete a tier, you are presented with 3 upgrade options: increased damage when punching, the ability to throw stars upward, or the ability to throw stars horizontally. You only get to pick one, and then you are immediately tossed back into the game. While each of these skills is potentially useful, none of them have a drastic impact on how the game is played. However, each new tier you complete opens up a new set of options.

Opening tier 2 allows you to pick any of the remaining options from the first tier, or any of 5 new upgrades. Among the new upgrades are the ability to fall 20% further without taking damage, the ability to punch through solid blocks, and immunity from being knocked back by enemies when damaged. Each time you make a selection, it affects the next set of upgrades that appears, and each higher tier offers more substantial upgrades.

On the 3rd tier, you have to make a choice between taking a valuable upgrade or unlocking the next set of more powerful upgrades when you reach the next tier. Get good enough, and you can stay alive to unlock skills like a high jump, immunity to spikes, the ability to kill an enemy with one hit (this upgrade is happily named God Hand), and immunity to fall damage.

Since the player is limited to the number of upgrades he can gain on a given playthrough, and since the available upgrades are dependent upon previous choices, the game offers a great deal of variety from one playthrough to the next. Just don’t forget which of the upgrades you purchased; you don’t want do drop down onto a spike block if you haven’t purchased the spike immunity upgrade.

Other modes include an Expert mode that has more complicated level layouts with less solid ground, and it scores players on depth rather than enemies killed (although you still have to kill enemies to open up new tiers). And, for those who really like toying with the upgrade system, there is the Karma mode. Playing the regular modes builds karma points which determine how many upgrade tiers are available when starting a new game in Karma mode. With 5 karma points, you can spend up through 5 tiers of upgrades, and start a new game with all of them. Be careful though, because there are no health-restoring tier transitions here, making this more of a survival mode. Also, each play of Karma mode reduces your karma by one.

Many of the game’s mechanics aren’t spelled out for the player and only become fully realized after repeated playthroughs. The upgrade tree, for instance, only makes sense once you have played a few times and completed a couple of tiers. Also, gnarled trees occasionally appear in the environment, and they each have one tiny white pixel attached to them. Touching one of these dots adds a single throwing star to your inventory.

Even your life bar isn’t directly explained. Rather than a typical meter or row of hearts, you have constantly changing text and numbers near the top of the screen that display humorous probability statistics (which cycle far too quickly to digest during gameplay). The size of the number is essentially how much life you have left, which lets you know how much damage you can take from enemies, spikes, or fall damage. Once you get down to the last couple of hits, the number displayed will be considerably smaller and a panic alarm will chime in the background, getting louder as you get closer to death. Your ultimate probability for success? Zero, of course.

Leaving things unexplained doesn’t have a negative impact on gameplay, however, as the player is able to intuit the game’s structure and mechanics by replaying the game. Early failures lead to short gameplay sessions, making the penalty for death very low. The penalty for failure actually increases as you get better at the game. Once you get a few upgrades under your belt, you want to try to protect them, but the game just keeps throwing more at you the deeper you descend. Losing a large stack of upgrades requires substantial repeated gameplay to earn back. This, in turn, is motivation for the player to continue, as the risk-reward system continues to pay off no matter how good you get at the game. This also supports gameplay variety, as the player is free to experiment with different upgrade combinations on future playthroughs.

Probability 0 was developed by Droqen (a fellow with the actual name of Alex Martin), a Canadian developer based in Toronto, Ontario. Droqen is the creator of numerous Flash-based titles, as well as some experimental games as part of the Ludum Dare 48-hour competitions, and most of his games are offered free of charge. Probability 0 was initially released as a freeware title, but this updated and improved version was his first commercial release. The game was offered on its own or as a bundle with 3 other games: Starseed Pilgrim, Pirattitude, and Fishbane.

Starseed Pilgrim is a strange game where that places you in a minimally-populated world and leaves you to plant seeds to grow new platforms of varying sorts to reach new heights and new levels. The game is accompanied by audio from Ryan Roth.

Pirattitude is a party game for up to 4 players, designed in conjunction with Jason Kaplan of JPK Games. Players dodge falling barrels, bombs, and other objects, while attempting to collect gems. Along the way, players can hide in barrels, shove barrels to crush other players, and avoid explosions which slowly wear away the bottom of the ship.

Fishbane is a challenging puzzle-platformer starring a deep sea diver who can toss and ride his own harpoons, which he uses to explore environments, press buttons, and solve puzzles. This is an expanded version of the original Flash game, featuring several bonus levels designed by Droqen and other indie game developers.