yes. usually it has something to do with how good your device is and how many monster there are on the map. Pack Size maps tend to have from a few to lots of ghosts. I try not to get a Pack Size so high that I get lots of ghosts. there are ghosts that follow you around, follow and attack, invisible, invisible and attack. if map has movement speed for the monsters, they will be hard to get away from. if they died from an Ice attack, that will slow their movement speed. if you do a search on Ghosts or Zombie monsters, there are some good posts. CuzegSpiked did a lot of research on the subject and posted his findings. I just did a search with @CuzegSpiked Ghosts, and he has 2-3 posts on the subject, check them out.