Here is the full list of all 10 Flashback achievements.
Receive a memorable commission.
Defeat the birds.
Watch Ending 1 and own 3 buffs at the same time.
Watch Ending 1 and gain 3000 Reputations in total.
Watch Ending 2 and live to Day 100 in the city.
Watch Ending 2 and gain 3000 Health in total.
Watch Ending 3 and reach to lv. 20.
Watch Ending 3 and gain 3000 Money in total.
Watch Ending 4 and only choose options on the left` or choose to give up reaching Day 20.
Unlock Ending 4 and only choose options on the left` or choose to give up reaching Day 20.