Add further Creature/Elite Creature/World Bosses variety

Particularly in open world mode - currently the sandworms/thumper-triggered landsharks provide excellent challenges and intrigue in an alien world. These could easily be established in missions too.

It would be a great challenge to face more variety in creature experiences and these could be varied in a number of ways.

For example:

1. Add more world bosses
- these could vary depending on region (e.g. in river biomes or in forest biomes), bringing other biomes in line with desert biomes
- bosses could be animal based or alien based, e.g. a large luminescent creature that stalks forest regions at night, giant anaconda in river biomes

2. More elite creatures
- more takes on the alpha wolf
- e.g. sabre toothed tiger, pterodactyl, large primate (yeti?!)

3. Day/Night exposure
- certain creatures only come out and are active at night time
- would give the players more reason to explore at night
- bioluminescent creatures/auroras/glowing minerals or crystals in subterranean regions