ROOKIES Trophy in Ghostbusters: Sanctum of Slime
Finish the first level.
How to unlock ROOKIES
The first level is considered a "training" level and is named as such. Simply reach the "Level Complete" screen to unlock this trophy. The end section of the level will be the area you started in, the main lobby. You will fight a purple twirling ghost who shrinks as you chop away at its health. After defeating this ghost, the level will end.