I personally did this during level 11 ”Apokolips, Wow”
As soon as you hit the x10 multiplier you’ll hear that magic pop, achievement unlocked.
Happy HuntingA Few Other LocationsHub quest Planti - Social
once you reach the last section of enemies to kill.Level 12 - Boss Fight Section
This is against Kalibak & his T - Rex Mech just keep & hitting the waves of his enemies attacking you. Then you can hit him as well if struggling for time/enemies to spawn in but do not kill him before you get your x10.