These druids belong to a group of (four) apparitions, which Mirror Images can turn into.
Druid's Apparitions have 25000 hitpoints. They cannot be paralysed. Moreover, they are strong against holy and ice damage. On the other hand, they are weak against death, fire and physical damage. These creatures can neither be summoned nor convinced. In addition, they are able to sense invisible creatures.
Druid's Apparitions yield 18870 experience points. They carry crystal coins, great mana potions, terra rods and sometimes other items with them.