Demons are not the best lategame idle. Goblin and undead both have an unlimited production gain over time upgrade for a flat cost, making them unrivalled on absolute long term.
You should consider increasing the difficulty and gold rewards of endless mode. As it is now I survived more than 30 minutes with very little efforts, only letting me lose out of boredom. And I only got 60k gold in that time while I could have had much more farming the campaign thanks to the trading crows.
Currently working on improvements to make Endless Mode a lot less dull and that includes the possibility of having bosses spawn! Thanks for the feedback!
 "Aisleen"){kind=icon}
 "Heart of Galaxy Beta"){kind=icon}
 "Tabletop idle"){kind=icon}
 "Save the Earth! - The Incremental -"){kind=icon}
 "Realm Grinder"){kind=icon}
 "Death Squad"){kind=icon}
 "Sentry Knight"){kind=icon}
 "Loot Hero"){kind=icon}
 "Defender's Quest (lengthy!) Demo"){kind=icon}
 "Super Duck Punch!"){kind=icon}
 "Bloons TD 5"){kind=icon}
Currently working on improvements to make Endless Mode a lot less dull and that includes the possibility of having bosses spawn! Thanks for the feedback!