You can display an animated sprite on a tile, such as an NPC, a monster or just some animated part of scenery, like a lamp. To do that, add a "sprite" property:

tile = .
sprite = boy.png

There is a number of sprites uploaded here already:

 boy.png  jack.png  bat.png  beast.png  hammer.png  box.png  bars.png  caution.png  eye.png  zombie.png  jello.png  ladder.png  robot.png  skeleton.png  weed.png  tree.png  pumpkin.png  pumpkins.png  light.png  mechanic.png