1. - Every X ticks, search in a radius(sphere or box) of Z
  2. - Choose random block from that array
  3.  
  4. if (Block != Material.AIR ) {
  5. if ((block.location +1 in Y) == Material.AIR) {
  6. if ((block.location +2 in Y) == Material.AIR) {
  7. //spawn zombie
  8. }else //find new random block and repeat
  9. }else //find new random block and repeat
  10. }else //find new random block and repeat