First, the "flying" rats were obviously there as a joke. Second, any one else get the Fallen Mines (medium 5 waves) glitch where during the 4th and 5th wave, the enemys would randomly become invincible?
to Randon:
the Doctor is actually really easy
just keep damaging him and once he reaches 990,000 (10,000 damage), he will always heal himself for 2,000,000. Time a shatter bolt so that he is stunned AND under 990k health and then use subversion. BAM. pwned :)