Let's Invade!

shoot'em up game for Commodore 64, 2016

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Story

4th December 2077: Earth has successfully made contact with alien life
forms. Luckily, most of them are friendly and welcoming. Humans and aliens
are working together on several planets of the Solar System to bring about a
peaceful galaxy and a better worlds for all.

One year later, an unidentified giant mother ship approaches planet Earth.
Scientists work hard to establish communication with the giant ship. The
translation of the strange alien signal is successful... but it brings bad news.
The new visitors have not come to Earth to help out. They are very greedy
and want to invade all planets. Planet Earth is at the top of their list.

A message from Planet Earth is sent back to the alien leader: Earth will fight
back! The mother ship beams out a psychedelic vortex field, and spits out
hordes of aliens… ready for the invasion. Planet Earth beams mobile military
bases, and prepares to do battle with the aliens inside the vortex field.

Instructions

This is a fast-paced “Space Invaders”-style game with a psychedelic
sound+vision twist. You fight aliens inside a moving void, with optional in-
game trance music or in-game sound effects. The aliens can be selected as
either transparent (made of checked squares) or solid (blocky aliens). Select
the preferred sound and graphics options from the title screen, then press
FIRE to play.

The object of the game is to shoot wave after wave of alien invaders inside a
vortex field. Move your mobile military base at the bottom of the screen, and
shoot laser beams at the aliens. The more aliens you shoot, the faster each
remaining alien will move. Your scoring depends on which alien you hit. The
Title Screen displays a list of points awarded for certain aliens.
The points are based on alien type, not colour.

During each wave, after the aliens have moved to their sideways limit, they
will move down towards you. However, if you shoot rows of aliens to the very
right or the very left, the remaining aliens will NOT make a complete move
across the playing area. They will instead move downward, after they have
moved their own set horizontal distance. The aliens also drop bombs on your
base. Speed and timing is crucial to your success!

The Levels

After you have completed a wave of aliens, you will be moved on to the next
level, and a new wave of aliens will appear on screen. The level setup is as
follows:

Levels 1 to 5 – All aliens require one hit to destroy (EASY). Only red, green
and blue aliens appear on-screen.

Levels 6 – 10 – Two hits to kill an alien (QUITE EASY). A medium shade of
red, green and blue aliens will appear. Their colours are pink,
light green light blue.

Levels 11 – 15 – Three hits to kill (MODERATE). The light coloured aliens
will appear. They appear as (yellow, white, cyan). The darker invaders will
also be on-screen.

Levels 16 – 20 – 1 hit to kill, with faster alien bullets
Levels 21 – 25 – 2 hit to kill, with faster alien bullets
Levels 26 – 30 – 3 hits to kill, with faster alien bullets
Levels 31 – 40 – Mixed, and even tougher

Power-Ups and Extra Lives

Due to the fast-paced nature and high difficulty levels in later levels
(especially when aliens become super-fast), there are special aliens
that give you power ups:

If you shoot an orange alien, you'll be rewarded with power-ups / power-
downs. It is compulsory that every alien is shot in each level, including the
orange and purple aliens. The power-ups are as follows:

Default Base: A power-down, which will restore the player's base to default
power.

Faster Base: Speeds up the mobility of your base. Once the player's base has
been boosted to maximum speed, the next similar power-up will not take
effect.

Faster Bullets: Speeds up the firepower of your base. Once the player's base
has been boosted to maximum firepower, the next similar power-up will not
take effect.

Super Shield: This power-up shields your player from enemy bullets. The
power-up is temporary, and can be lost when an invasion occurs.

Tranced Out: Freezes the aliens for a short time. Their bullets will still
drop.

Blackout: Removes the void for a temporary amount of time, to make aliens
(from transparent mode) easier to see while you battle against them.

Smart Bomb: Temporarily armed to the player's base. When the base changes
colour, pull DOWN to destroy all aliens.

Extra Lives: Purple aliens will award you with extra bases. However, you
cannot exceed 9 bases.

LOSING A BASE

You will lose one of your bases if any of the following occurs:
- Your base is hit by an alien bullet
- An invasion occurs (i.e. an alien reaches the very bottom of the screen).

Hints and tips

- If you get faster bullets, try to avoid being hit, otherwise you will lose
  the power-up. Later levels may require this power-up, unless an alien
  mischievously gives you the DEFAULT weapon, where all is lost apart from
  the base.

- If you are awarded a Smart Bomb, when nearly finished on the first level,
  save it for the next level.

- Blast the aliens as quickly as possible. On later levels, try to find a way
  to weaken the top row of aliens first. There are gaps in between the aliens
  to make this possible.

- Survive and win!

Can you complete all 40 levels of 'Let's Invade', and defeat the aliens for
good?

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Some useful keyboard shortcuts
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       [PAUSE] - stop/continue game
          [F9] - quick load game state
         [F12] - quick save game state (still stored after leaving the site)
         [F11] - toggle fullscreen mode
  [ScrollLock] - quick switch control ports
    [PageDown] - make a screenshot (320x200)