The Monster the Monk is fighting is called a Whispering Phantasm. Usually, they are not strong enough to hurt a pony, but this Cleric is taking no chances. Phantasms are vengeful spirits who cling to the mortal world, and whisperers are small, weak ghosts which 'whisper' in Adventurer's ears and fill them with doubt and loathing in an attempt to isolate them from their Adventuring party.