Originally Posted by HLW
That's the same one that I was wondering about.
I've just noticed that all the towers/turrets are featured on the train on the start screen, so you can watch and see what they all do, which is useful!
But the pink smokestack doesn't appear to do anything obvious. It looks the same as the turrets on the flying enemies, but it doesn't look like it's firing on them.
I've already submitted V1.1 update with a few cool features (flamethrowers, a new enemy, a ZOOM window for when placing turrets on the train) and fixes, but I'll definitely add a turret key to the help menu in v1.2 (and make sure people can find the help menu).
FYI. The purple turret heals anything in a radius - carriages/engine/towers. Once you have that, using the water tower to heal you is less critical, though a single heal turret can't heal itself. I guess its inactive on the attract screen since I made the train & carriage invulnerable. I'll fix that in v1.2 update also... let them at least take some damage so the heal turret can do its work. You may notice some enemies having the same turret.