Create the event deck of 6 randomly chosen cards marked with Level "I".
Create another deck of 6 randomly chosen cards with Level "II".
At the beginning of each combat phase, the (new) start player draws 1 card from the event deck and collects the bonus, does the bonus action for free, puts the ancient ships in any chosen territory or the ancient/galactic center upgrade in the common area.
Then he draws a replacement card from the level "II" deck and shuffles it into the remaining cards. If the level "II" deck is empty, shuffle a level "III" card into the event deck instead.
If the "END" card is drawn, the game ends after that round. Normal ending after round 9 does not occur, if you play with event cards.