At later stages, instead of just *more* raiders... Might I suggest a small group of raiders that lands right in the middle of your stuff, already combat-ready and attacking?
Maybe target them at a concentration of your people (or where they are projected to be in ~5 seconds), or maybe target them at buildings. If they land extremely close to someone, maybe stun that person for long enough that the raiders can bolt for cover or get a couple shots off. After doing enough damage / wasting enough time / suffering enough casualties, the raiders try to return to where they landed and take off again (implying that their dropships were left where they landed). If you blow up the dropships or if it's too dangerous, they escape off the map.
Counters to this: Well, suddenly you need turrets everywhere, not just on your borders. Naturally these attackers can't land underground or inside a building, so those are partially safe.
Definitely late game only, but I wouldn't mind seeing this in Cassandra (not just Kassandra). Probably not Callie, unless it was just like...one or two guys AND later in the game.
Yeah, pirates on board of some kind of drop pods. Just two suggestions :
- a message prior to the pod arrival should be displayed (something like "your sensors indicate that a manned pod will land soon inside your colony)
- cave breaking pods would be awesome (I mean pods that could land inside a dug colony)
I have a better idea.
Why bother with raiders dropping in at all? They should just drop a goddamn space rock on top of 1d6 of your colonists from orbit and have done with it![/sarcasm]