Taking a Step Back...

The mastery reward of this mission is dependent on the choice made regarding your team's approach.

Intervening rewards the Principle-ist mastery.

Waiting and watching the situation for the moment rewards the Flexibility mastery.

Both options have your team approaching the train, which has Spoonists and Remodeled Bicrons pouring out, while White Tiger gang members start on the opposite side of the train. All enemies have to be defeated to win.

Each option has unique dialogue before the mission starts. Some of the named enemies have unique dialogue when Ray and Heixing enter their view. When Intervening, getting on the rooftop near your team's starting position also reveals some dialogue.