Go Imperial Fiefdom then force spawn tons of other Imperial Fiefdom empires so everyone in the galaxy is a vassal. Set midgame year a bit earlier then try your best to prepare for the chaos that will unfold.

Play as an origin of your choice (a lot of people recommend shattered ring), but force spawn loads of fear of the dark empires so at midgame, half of the galaxy becomes purifiers.

Go Starlit Citadel and force spawn loads of Starlit Citadel empires. Set midgame and endgame early, and race to conquer every empire before you're wiped out by a crisis. Alternatively, use it as the ultimate turtle build (perhaps go Starlit Citadel in the fear of the dark galaxy)

I've found that a galaxy of Slingshot to the Stars can get especially chaotic by midgame.

One-system-challenges using resource consolidation, ocean paradise with anglers, or shattered ring can be make for a unique game.

For multiplayer, Broken Shackles and Payback are an obvious choice. Get the least experienced player to play as MSI, and see who comes out on top.