We'll make this educational as well:
All the MAP format stores in terms of entities is their position, size (if applicable), and their name. Nothing else. You could make up an entity called blahblahblah and BSP would be fine with it. However, all of the entity processing is done when the map is loaded, so the game wouldn't be that happy about it.
That said, adding entities is a snap. Just go to the game you wish to edit's folder in BSP, go to the entity folder, and edit the entity file.
It's arranged like this!
(Where things in brackets are optional.)
/*QUAKED entity_name (val val val) [(val val val) (val val val)] ? [FLAG FLAG FLAG...]
Help text, help text, help text.
*/
Entity name is, of course, the name of the entity as the game sees it and as BSP shows it.
The first three-value tuple represents the color of the entity as seen in BSP. Standard R G B, where each value is between 0 and 1.
If the second tuples are included, it means the entity is point-based instead of brush-based (i.e. it doesn't need you to define a brush in-game like you do with doors)
The second tuple (if included) represents the offset of the entity in X Y Z, I think. Doesn't matter, just make it the negative of tuple number three.
Tuple three is the size of the entity in-game, in X Y Z. Make all three 16, if the entity isn't brush-based.
Past the question mark, the entity's flags are defined. What they're called doesn't matter- all that matters is whether or not the mapper checks them and what order they're in. So get the order right. You can use helpful resources (like gamedesign.net) to see what the flags are.
Helptext is in no way required, but helpful.
That's all. You should be able to make the entity now. Go ahead.
EDIT: Oh, and target_earthquake isn't brush-based.
