SPOILER:
the reward at the end is predetermined
for the biggest bonus choose the following order
1: blue(10) 2: red(20) 3: blue(30) 4:red (40) 5:red(50)
you should make the fire a splash effect, or contagious ie. if you slow the tower on fire and a house passes that's not it catches on fire, better arrow upgrades would be nice, past round 15 their almost useless
 "Monster War Zone"){kind=icon}
 "MonsterCraft"){kind=icon}
 "My Tower Defense"){kind=icon}