The reason why I don't like "It".
There are no rules. Pennywise can do anything he wants, take any form and alternate the universe as he pleases. Also whatever Pennywise does only seem to affect the main characters while the rest of the world is completely oblivious to the monster. Yet, he never kills all the main characters even though he had the opportunity to do it 100 times. Whenever the characters seem to win, it's just because Pennywise is playing along. So nothing ever matters except at the very end.