"Wtf did that boss just build a sentry???" - An unsuspecting player
This plugin adds the ability for bosses to place customizable sentries in attacks. All you gotta do is set the attack_type in an attack to "7", and this plugin will do it's thing.
SF2 Modified is required to compile it of course. Grab it here: https://github.com/Mentrillum/Slender-Fortress-Modified-Versions