Patterns of Asteroids to Appear in Levels

I began watching a playthrough of "Epistory" to get a better idea of the kind of Types of obstacles that could appear in game -

Obstacle 1 : Moons -

Stationary asteroids that aren't moving at all could be called "Moons." Their design could be spherical and uniform. Moons are the main obstacle at lower levels when players are getting familiar with the game.

Subcategories of Moons -

"Moon : Vulcanian" - Hot, firey moons. When the player decides to kill them they blow up and destroy all other enemies on screen at that moment. They act as a resource players must choose to use wisely.
"Moon : Cryogenic" - Icy moons which freeze all obstacles on screen for a certain amount of time.
"Moon : Terrestrial" - Normal static moons which are destroyed for points. In game for lore, the reason they may need to be destroyed is to allow the player build a space station of some sort.

"Moons as a Resource" -

At later levels on planets that have life on it maybe players shouldn't destroy moons as it would affect waves, etc. Choosing to preserve a moon by not senselessly destroying every object to appear on screen could help players think before they type. If any kind of base building mechanic is implemented later on - where players can set up stations on certain planets to farm in game currencies that they can earn passively having a good relationship with the creatures of that planet by not destroying an essential moon could allow them to set up a base on such planets.

Obstacle 2 : Asteroids -

The main obstacles in the game that move towards the player.

Subcategories of asteroids -

"Asteroid : Vulcanian" - Fiery asteroids that must be destroyed from far away. If they are too close to the player when attacked they will damage the player regardless. They also have an "Area of Effect" feature which destroys nearby
"Asteroid : Cryogenic" - Similar "AOE" feature where they slow down nearby asteroids on explosion. These asteroids may be less harmful damage wise but reduce the speed of the bullets the player shoots for a certain duration.
"Asteroid : Terrestrial" - Normal type. Most common asteroid to be found.
"Asteroid : Gargantuan" - Largest asteroids which when broken split into smaller ones. If the word is "Butterfly" to destroy it, it splits into 2 asteroids - "Butter" and "Fly."

Spawn types of asteroids -

Random spawner as seen in the game right now.
Asteroid belt (for survival mode levels) - A large infinite number of asteroids spin around the periphery of the screen. As the level progresses asteroids break off from the asteroid belts and come towards the player.

Obstacle 3 : Comets

The fast moving smaller obstacles that always require lower letters to destroy than the asteroids of the same level.