Lol they used the same strat on us last night too, I was dumbfounded as I never saw anything like it before.
This was also on Leviathan, the actual game was here: http://pantheon.demigodthegame.com/game/668693/player/32715/
Same strat. What had us going is that we were doing well and ahead on the kill count. So we were saving up for some creep upgrades and getting prepared to push in a few levels (most of us were around level 8 at this time).
During most of this, _Shadow was just chilling out of range of the flag I was near for most of the game and I should have known something was up as he wasn't doing anything himself but his nightwalkers were tearing our rook a new one.
_Shadow vanished after a few minutes and before I knew it, "you're citidal is under attack". I checked it out and it was already at 2/3's and dropping fast. We had the tower I upgrade at the time. Game was over.
It was a great game just for the fact of experiencing something like that.
In hindsight our regs should have gotten a clue and ported back to cit immediately to mine. There was no time for creep upgrades, war score was not that high at the time. Pretty sure they snuck down the portal lanes in Leviathan which is a great way to not be noticed as most of the action is in the inner lanes. So there was no warning at all, except for the fact that _Shadow's nightwalkers were tearing up our rook prior to the event.
Only defense I can think of for this is focused AOE on the minions with at least 2 other people pushing to keep the demigods honest. They do this relatively early and creep upgrades would not help you. With the amount of dmg they were putting out, I doubt tower upgrades would have helped either. Like RapierX said, most of what you guys have said would not work. It was way too early in the game for any effective citidel/creep upgrades. The only things on our cit were their minions, I never even saw their demigods at all in the end. I mean technically all the demigods could just sit in their own base and just send their minions down the side lanes. Personally I think they chilled in the outside lanes and maybe ate a few tower blasts so they could send their minions in without being damaged, then just sat back and enjoyed the show.