Setting up challenges would be good for an individual achievement goal
A challenge game would have set parameters and they would be the same each game. A typical challenge game might be, there is a large AI player in the centre of the map, there are 4 players equal distance from the AI player (simular shape to the number 5 on a standard D6) The players have to work together and eliminate the AI, assume the AI is equal to the combined strength of the 4 players, and getting stronger.
Plot twist! Players have rankings in the challenge, and they can attack each other, so if you want to get number 1 in the challenge, you have to eliminate the AI and also have more stars than your challenge competitors. Completing the challenge alone will be tough enough on its own without players turning on each other. When you complete a challenge, you will get (similar to a badge) showing that you have completed the challenge, and the colour on the badge will show what position you placed on the challenge
Completing the same challenge a second time will not get you another badge, but if you place higher than you previously did, your badge will change colour to show your top ranking in the challenge. If you complete the challenge in position 1 x amount of times, you would get the top award for that challenge
other challenges might be
blue player has to take out yellow player, but red player can’t be eliminated. each player would have a similar goal trying to eliminate one player and protect another!
There are 5 golden stars in the system, hold each star at the same time to win, but the golden stars have negative effects, one gives you negative manufacturing across your entire system, one gives you negative 10% economy etc. You can only claim one star each day!
other challenges might be available during standard games eg.
win the game, but have less economy than 2 players
don’t place first, second or third, but have the highest science
destroy at least 100 ships from 15 different players in a 32 player game
break 4 alliances in the same tick
have half the players in the game in a formal alliance with you at the same time
have more science than economy
challenges would only be open to premium players
some challenges would award players for doing extremely well and winning by a long way
other challenges would give players something to work for even if they are losing and thinking of quitting, this might prevent some quitters! and other challenges would be games themselves where you are stuck in a bad situation and had to get your way out of it!