How to win against Endless ?

Solo play
-Create a custom Civilisation will all the defect you can give to get under -195 :D
Then give it to the AI to play
you take your best military based build or custom

-Select no pirate, duel galaxy 2 player, fewest connection and short line as possible and take cluster so you can block ai expansion which is faster than your even with the worst malus of the universe

-Try to take in prioity the way to explore beyond the wormhole due to few connection between those cluster and create a chokepoint. and then stack unit like crazy in the choke point then get his strategic ressources under blocus once you take a little tech military advantage.

Don't forget you can save and load.
GG Now you know how to get the achivement like me.