@manwithabook: there's no reason to grind for levels. There are a few awards that are useful (like the horde), but its not too tricky to get them. The levels, otoh, are pretty much useless.
@Domand: You lose 3 smog every time step. But if you run a lot of coal, or petrol fueled vehicles, or farms, you'll be adding more than you lose. Turn off coal stations, switch to gas vehicles, and keep your farms under about 15.
@thatotherplayer: it is possible to get a warrior all the way on little forrest. Its tricky though, and you need the two time awards, and probably a bunch of others too. On race track I sincerely doubt it.
@thatotherplayer: to make a necromancer, you need to level a regular mage up to level 10 (2000 xp) and then choose necromancer. Holy light is better though. You get a range bonus, which makes them much more effective imo.
@panding, that's not a bug, its the way its meant to work. You have to build a less tight maze.
I make one kill zone, using darts and power ups and frost towers, and then have my maze loop back to it once. Works fine, regularly get less than 20 min.
 "Loondon"){kind=icon}
 "ClueSweeper"){kind=icon}
 "Back to the Cubeture (1)"){kind=icon}
 "Level Up!"){kind=icon}
 "Protector III"){kind=icon}
 "Super Energy Apocalypse : RECYCLED!"){kind=icon}
 "Monsters' Den: Book of Dread"){kind=icon}
 "Frontier"){kind=icon}
 "Protector: Reclaiming the Throne"){kind=icon}
 "My Pet Protector"){kind=icon}
 "Desktop TD Pro"){kind=icon}