I really enjoy this game, maybe you can add decorations that are available to buy for the castle or a costume shop that you can buy outfits that can be a reference to another game like link from legend of zelda for your characters.
survival= take the tazer gun, unlimited ammo and then find a way to autoclick (auto clicker or something on your mouse) then leave! made it to wave 40 easily
 "Cube Escape: Harvey's Box"){kind=icon}
 "Idle Raiders"){kind=icon}
 "Mushroom Madness 3"){kind=icon}
 "Just Type This"){kind=icon}
 "Toss the Turtle"){kind=icon}