ZX Spectrum game · play free
Jelly Storm
Defend the moon base from waves of space jellies. Watch for the red divers that break formation and swoop straight at you.
In short
- Jelly Storm is an original fixed-screen shoot-'em-up for the ZX Spectrum 48K and 128K.
- A formation of 24 space jellies sways across the sky and drops a row each time it reaches the edge.
- Red divers break away and steer towards you: they're worth 150 points.
- The waves get faster and the stings thicker up to wave nine.
- You have three lives, and the game ends early if the jellies reach the ground.
How to play Jelly Storm
Your gun base moves along the bottom of the screen. Above you, four rows of six jellies sway from side to side, stepping down a row each time they touch an edge. The fewer jellies are left, the faster the formation moves, so the last few are always the hardest.
Jellies drop stings as they go. Every so often one turns red, breaks from the formation and dives at you. Shoot it on the way down for a big bonus, or simply get out of its path.
Scoring
| Target | Points |
|---|---|
| Bottom row jelly | 10 |
| Second row | 20 |
| Third row | 30 |
| Top row | 40 |
| Red diver | 150 |
How the waves change
Each wave starts lower, steps faster and drops more stings, from two at a time at first up to six. From wave four the stings fall faster, and the divers come more often and move more quickly. The difficulty stops rising at wave nine, but by then the jellies start very close to the ground.
Tips
- Thin out one side first. A narrower formation has further to travel before it steps down.
- Keep moving. Stings fall straight down; a moving target is much harder to hit.
- Watch for red. A diver turns red before it leaves the formation, giving you a moment's warning.
- Don't chase the top row early. Low jellies are the ones that end the game if they land.
How Jelly Storm was made
Jelly Storm is written in Z80 assembly and uses no Sinclair ROM routines, with its own font and interrupt handler. The formation is drawn straight into the screen's character cells, while your gun, the shots, the stings and the divers are sprites drawn over the top. In testing, an autopilot reached waves three to five on both the 48K and the 128K, and the game holds 50 frames a second even at phone size in the browser.
On a 128K the AY chip plays "Moon Base Alpha-Bet" on the title and "Jelly March" in game, which rises in key and speeds up wave by wave until wave nine is twice as fast as wave one. On a 48K you get the original beeper march.
The controls cover the three main layouts of the 1980s, so most keyboard habits and joysticks just work. Our guide to Spectrum joysticks explains them, and playing Spectrum games online covers phones and gamepads.
