If you leave the building and then come back to the first room, the janitor will listen to you (or maybe he falls in love with you? It's hard to tell what the person who made the game meant)
My strategy was to invest in spawn rate and health of my minions, and hide behind them so that they soak up bullets while I am at the shadowdemon. It worked pretty well for me.
For some reason, after I completely beat it (on easy) I decided to make the place a utopia. And this game's version of a utopia is pretty messed up.
Everybody is a soldier. Everybody. There is a force capable of holding back 2000 zombies on guard, even though there are no more zombies. The schools have become Military Retraining Grounds, where anybody new who comes is turned into a soldier.
Since everything has been discovered, all the laboratories were replaced with bars, so there is no more scientific progress; only drinking. What kind of a world has it come to?
For unlimited money, buy the things that shoot automatically, put it on endless mode, then leave for a while. Come back, upgrade them, leave, and repeat.
 "Doodle God Blitz"){kind=icon}
 "Bear in Super Action Adventure"){kind=icon}
 "Drop A Beat, Giuseppe!"){kind=icon}
 "Soccer Physics"){kind=icon}
 "W-Zone"){kind=icon}
 "Ultimate Santa Battle"){kind=icon}
 "Fixation"){kind=icon}
 "Robot Wants Ice Cream"){kind=icon}
 "Rebuild"){kind=icon}
 "Memoir Text Adventure"){kind=icon}
 "Kamikaze Planet"){kind=icon}
 "Meat Boy"){kind=icon}
 "GunBlood"){kind=icon}
 "Castaway Island TD"){kind=icon}
 "Star Claws"){kind=icon}
 "Kids Vs. Santa"){kind=icon}
 "Sierra 7"){kind=icon}
 "Karoshi : Suicide Salaryman"){kind=icon}
 "Midas"){kind=icon}