frekk
Scourge of St. Lawrence
For the Svartalfar, I thought what might be better than an illusory defender is a hidden commander and hidden fort (using the same mechanics that hide resources - you'd need a tech to locate these forts). Secret strongholds, hidden by illusion magics. This would be a real pain in the butt as these strongholds couldn't be claimed until the technology to reveal them was discovered, and even then, the commanders themselves would need to be spotted by something that can see hidden.
Alternately, I thought that just a hidden commander might be interesting for the Sidar or maybe the Calabim, one of the undead civs. Like a haunted fortress. You could see it but you'd be subject to unseen attacks in the area from the undead spirits inhabiting it and you wouldn't be able to claim it until you could bring in a spotter who can see hidden, and root out the "commander"/entities.
Alternately, I thought that just a hidden commander might be interesting for the Sidar or maybe the Calabim, one of the undead civs. Like a haunted fortress. You could see it but you'd be subject to unseen attacks in the area from the undead spirits inhabiting it and you wouldn't be able to claim it until you could bring in a spotter who can see hidden, and root out the "commander"/entities.