In shoot-em-up's, that is.

My current project is another Blipfighter shooter, a revamp of a thing I started last year.
The idea being that the aliens evolve via natural selection.
If you call being blown up by the player's ship 'natural'.

But to reiterate my main question: What makes for an interesting alien?
I ask this because the new alien's AI routines are generated from mutated code rom successful 'parents'.
An successful alien is one which scores a high 'fitness' value.
Here is how fitness is currently defined:
* Score 1 point per game tick for merely surviving.
* Score point for firing a bullet, equal to the bullet's damage rating.
* Score point for having a bullet hit the player, as above, but total fitness is also boosted by 50%. This is because damaging the player is the aliens principle function.

UPDATE: -1 point for flying into the side of the screen.

The problem with the first definition is that it may encourage aliens to be inconspicuous, basically hiding in the corner hoping that the player won't see it, and racking up fitness based on longivity.

The problem with the second definition is that after a dozen generations, the screen is just a blanket of small bullets that are difficult to avoid. This is basically because there's no advantage to not firing as rapidly as the weapon will allow. Now I kn

ow the game is supposed get harder as you go along, but it seems to actually evolve too quickly.
I should also mention that the limits placed on rate-of-fire and bullet damage are the same for both the player and aliens; Firing has a rate-of-fire cycle that can only be improved with power-ups. If an alien has power-ups it also increases its value, wh

ich gives the player more money and limits the number of aliens on screen at once.
So it _should_ all balance out.

In an effort to keep aliens interesting to fight, I also had the following in place:
* Halve the aliens fitness if it escapes off the bottom of the screen.
This was to discourage aliens from just simply dropping out of the level without doing anything interesting.
The main problem with that is that if there are two identicle aliens and one drops off the level and the other is blown to smithereens by the player, the one that was destroyed
actually scores a higher fitness. Maybe that's not important? There's no point in halving the fitness for destroyed aliens as well.

Now, all this is all very well for creating successful aliens that are good at blowing the player up, but what we want are interesting aliens with interesting behaviour.
How to translate this into the fitness value?
Current ideas include:
* Score fitness if a players bullet narrowly misses the alien. This will encourage the aliens to move with unpredictable behaviour.
* Score fitness for shooting at but narrowly missing the player. But this may just encourage the 'blanket of bullets' problem above.

Need more ideas! Help appreciated, and the game executable is available for playtesting; just contact me.

I'm also aiming to have a lot of intricate power-ups for the player (and the aliens).
This has been described as a kitchen sink statement, but I stand by it: I want to have in more power-ups than X-Out, Xenon 2 and R-Type combined, whilst simultaniously ripping off all their ideas and keeping everything relevant.
Currently you start with a 'blaster', and can improve:
* The rate-of-fire.
* Damage. Increases damage but also increases the amount which your ROF cycle decreases, and how fast your energy decreases.
* Burst. Each purchase of Burst splits your shot into a sequence of smaller blasts, so if you buy it enough times you get a machine-gun effect.
* Twin. Fires two adjacent shots (but decreases your Rof-Cycle twice as much)
* Added in version 0.4: Tri-shot; Quad-shot.
* Added in version 0.3: Charged shots, which can also be converted into fireballs.
* Added in version 0.6: Various auxillary guns.

Also:
* Energy. You have a main Energy capacity that powers the ships upward thrust, armour regeneration and your blaster. Your total energy can be increased. If your energy reaches 0, your main gun is locked out until Energy can reach 50%.
* Charge. Increases the rate at which Energy recharges.
* Armour. For taking damage. If armour reaches 0 you blow up. Armour is repaired if your Energy bar is at 100%.
* Shield. Each level of shield decreases incoming bullet's damage by 1. So actually, if you buy enough levels of this you can simply ignore the 'blanket of small bullets' problem detailed above.
* Added in version 0.5: Armour repair.

There are two balancing factors here:
1. If you power-up too quickly without giving attention to ROF and Energy levels, you will find yourself with a huge gun that can only fire for short periods of time.
2. The aliens can have any power-up that the player can. I am hoping this will develop into some kind of evolutionary arms race.

rking electrical zap. Raiden-style thick laser beam. Etc.
* Pods of various kinds; by-the-side, orbiting, attaching-on-the-front-like-R-Type.
* Side shot
* Smart-bombs, most importantly including the 'Death Blossom' which has been in all my other Blipfighter games.

Again, ideas wanted. Power-ups should be as fundamental as possible; for example in the way I split the basic blaster up into several different components.

UPDATE: At the moment aliens learn very quickly that twin-shot is a good thing to have. Now we don't want every alien to have twin-shot, so possibly I need to lower their energy to a miserable level - in an attempt to force them to evolve energy-management. Appears to be fixed.