Currently, when encountering a rogue, I come across two scenarios in my games:
1. Mid Game
The rogue appears at a location that already has some defenses in place and destroys a few buildings before being wiped out. There seems to be nothing that I can do to prevent at least the loss of some buildings (is there a way to intercept underground attacks?), although loosing a couple does not create a problem in this situation.
This scenario does not pose a problem aside being a bit boring maybe (might be resolved simply by scaling up the number of simultaneous rogues, though).
2. Early Game
The rogue appears before a significant amount of military buildings are in place. Plopping them down then is mostly ineffective, since many monsters seem to match or exceed the range of barracks (and maybe even helipads - I haven't checked) and simply pick off the under construction buildings one by one (if I don't have the crowns to plop them down in significant numbers that is).
Thus the fact that rogues comes without warning (or can't be seen wandering on the map before coming into attack range - this might actually be cool and a good use for early game sonar) and apparently one-shot every building they encounter, makes them a bit too strong/crippling early-game in my book, especially if more then one decides to show up.
TLDR
Thinking about this while typing, my proposal would be to have monsters roam the map, have them picked up by scouts/sonar and potentially generate a warning similar to what has been done for thoraxian tunnels recently.
This way the player can prepare without a kinda unnatural warning like "monster incoming in X" t being necessary.
Having them picked up and notifed to the player by scouts/sonar and potentially picking them up earlier by manual scouting/sonar might even enhance the exploration aspect of the game and create a meaningful use for sonar early-game in the first place - something the game is lacking at the moment in my opinion.
Thoughts?
EDIT: Mantised
here and
here.