I've posted this in Idea section (https://www.games2gether.com/endless-space-2/ideas/1485-e-n-f-e-r-challenge-mode), but as a more major concept I decided to post it on forums as well. And becouse I realized the Idea section is a bit ignored. So:

New game mode. Similar to Blizzard's brawls or CivFanatics Hall of Fame. They are special prescripted matches. There are many challenges, but only one active at time. One challenge lasts one/two/three weeks, and after that time, it gets expired (maybe added as a scenario) and the new challenge appears after that or after some break. All players can play the challenge once, and everybody have exacly the same setup: map, settings, everything... All you have to do is win this game and after the challenge, your score is compared with the score of other players.

The E.N.F.E.R. challenges may not only be basic matches like those that may be generated in typical match. They may have special events, special map conditions, special rules and ways to win and to score. Maybe sometimes they could be played in co-op with another player(s) during special events. The only static rules is game speed and it's normal.

Possible rewards:

 - Steam achievements.

 - Faction ship skin for winning any challenge.

 - Leader skin for be top X in ranking of any challenge.

Examples of E.N.F.E.R. challenges:

CRAVER CRUSADE

Available factions: Cravers only

Objective: Conquer all Capital Systems.

Scoring by: The smallest number of turns before win. Then the strongest fleet.

Special rule: Depleted planets are destroyed. Planets deplete 50% slower. Slaves are always killed.

ENDLESS PEACE

Available factions: Any but custom

Objective: Have the highest score by turn 120.

Scoring by: Game score at turn 180.

Special rule: Nobody can declare wars. Pirates are stronger and there are more of them.

UTOPIA

Available factions: Vodyani only

Objective: Get your Ark to Academy.

Scoring by: The smallest number of turns before win. Then the highest score.

Special rule: You can't build Arks and gather essence [one system all game].

SURVIVAL

Available factions: Any but custom

Objective: Survive as long as you can.

Scoring by: The largest number of turns before defeat.

Special rule: Your enemy Empire is sourinding you. They are Cravers and are much more stronger. They will declare a war at turn 50.

UNITED UNITED EMPIRE

Available factions: United Empire, Mezari, Sheredyn

Objective: Win in any way.

Scoring by: [idk]

Special rule: Co-op challenge for 3 players. They are in Alliance that can't be abandoned. Faction quest is disabled. Each player must play different faction.

Maybe nothing remarkably revealing, but I think that it would help put more life to the game and additional element of rivalry. What you think about it?

The rules may be very simple, just like regular matches, but everybody has exact the same conditions, even factions. Balance is secondary thing, sometimes the challenge is harder, sometimes easier, but every player has exacly the same chance to score. It's mainly random generated map, but everybody's got exacly the same map. Special rules may have place during special events and then it's easier to maintain. The only problem may be technical foundation for tracing those games and special UI in menu.