Chalenge: golems and starships!
Well, i made a special game starting in a dead end with 6 homeworlds and with a 30 planet map so i could make a massive chokepoint and get the trader goodies. The game was vs starfleet captain and golemite at level 9. I left the game running while i doing other things so i could build like crazy, ans ended up with 6 zenith generators, 4 super fortresses, and tons and tons of stuff that shoots.
Game was completed at 25 hours when the starships were starting to get overwhelming. I had time to do a lot of destruction before it ended though, including: the devourer golem, 4 ai golems, 4000 starships, and 560 000 other ships.
As for the challenge, the biggest pack i faced was when i destroyed the second ai homeworld station. It released 60 raid ships mk3, 60 leech ships mk3, 5 more starships, 1 armored golem, 1 avenger, and lots of friends. But i was very ready...
Note that the avenger is so slow that all its friends were already gone when it arrived to the party, so as far as the challenge goes, it wasnt part of the pack.