turn on custom factions, and make (choose weak hp race here) i prefer cultists because they cannot expand. Take away all positive skills in custom build. Add every negative debuffing skills you can find.

Choose a race that can make a really strong/fast rush early game. Necrophage, ardent mages and wild walkers come to mind.

Set game modes to fast and ai difficulty to endless, also make empires 2 and map small. Make the empires spawn right next together in the options. Choose the custom race you made absolutely horrible for the endless ai.

When you start the game focus on industry/science tech. Build up your era 1 buildings then just start mass producing units. Rush the ai while they're scouting about then siege their capital. Keep sending your units to their capital until they all are dead. Make sure it is past turn 25 though or you won't get the "quick out of blocks" achievement.

You just unlocked easy-endless difficulty achievements as well as the achievement to have a higher score than hard + endless AI for 25 turns. enjoy. (If done correctly that is).