This guide will let you know how to unlock the Legacy campaign (16 Secret Units) in Totally Accurate Battle Simulator.
You will need to find all secret units in the legacy map to unlock the Legacy campaign.
Open Legacy Map
The first thing you have to do is open the Legacy map in sandbox mode.
And click F to enable the free cam mode.
Blow Dart (Blowdarter)
You can find these units in the legacy faction sector.