prion

Aliens are infecting Earth with a deadly disease. You have been tasked to destroy all spacecraft that pose a threat to our planet. Please act fast, as your reward is based on the amount of uninfected land in each wave of enemies. There are an estimated 10 waves of increasingly harder alien reinforcements. Reports also show that the extraterrestrials possess a device that can alter the force of gravity. We have equipped your ship with fuel and altitude gauges, a scanner, a laser cannon , and homing missiles.

You can land the ship at the base to fully refuel your craft. Additionally, you get one homing missile and a spare life every 5000 points. The following 3D scans were just sent to us by mission control and show the aspect of each alien spacecraft that is part of the invasion force:

We have been able to determine the behaviour of each enemy vessel, except for the last one, the mysterous spacecraft. Be extremely careful around it. 

Ship	Behaviour
Seeder	A non-aggressive flying saucer that spreads the disease across the ground and plants
Drone	An aggressive spacecraft that becomes stronger after it destroys a mutated plant
Bomber	A non-aggressive carrier that drops infectious bombs that affects a very wide radius of the surroundings
Fighter	The professional killer of the invasion force. It is an aggressive spacecraft designed to shoot any form of life that is against theirs
Pest	A kamikazi-style alien spacecraft that follows and tries to crash into you
Attractor	An aggressive spacecraft equipped with a high-tech tractor-beam that pulls any spacecraft in its vicinities
Mystery Spacecraft	A secret new alien spaceship roumoured to have joined the invasion force,   and that may strike at any time. Beware, as it may have a  lethal new weapons system fitted.

Try and get a highscore of 140281 or higher in those 10 waves, that means you're better than me. Good luck! The future of mankind is in your hands.

Controls

1. Use arrow keys to orient the ship
2. Press Z to thrust spacecraft
3. Press X to shoot laser cannon
4. Double-press X to shoot missile

Source Code and Graphics

The source code for the game can now be found on github. The 3D graphics were made with the freely available Zarchy Engine for pico-8. Go ahead and give them both a star to show support 😊

Credits

This is a fan remake (or demake, or sidemake?) of the original Zarch(1987)/Virus(1988) game by David Braben.

Changelog

v1.1.6

• add HOUSE
• infected bush now gives 40 points, just like infected tree
• attractor beam reduces player fuel
• whole best score can now be seen (fixed identation)
• fix order of env objects

v1.1.5

• fix suicidal pests (hitting the ground)
• fix player losing multiple lives as once
• give 5k rewards when wave ends
• player now dies when it has no fuel and gets shot
• mini pest doesn't count to finish wave

v1.1.4

• fix shadow flickering (thx @krispykrouton)

v1.1.3

• fix major kill count bug (was counting hits as kills :S)

v1.1.2

• fix missile and enemy tracking considering wrapping map
• fix randomicity of spawns
• fixed bug where wave can end before all enemies are killed
• make fixed path ships only face a certain direction for the entire wave
• fixed jumpy spacecraft heights
• fixed bug where sometimes the death score of the kill didn't count
• it's 2024 not 2023
• make drones a little less likely to become mutant
• some performance fixes with particles

v1.1.1

• fix cartdata name
• fix randomicity of spawns
• make gravity changes a little lighter

v1.1

• add starting screen music
• first refinement of sound effects
• add levels 8,9,10
• add gravity and map change logic
• fix score when enemy hits the ground
• make missile have very high damage
• fix the routine relating to height in relation to the
• ground when attacking the player by drones and fighters