He used an upgrade – Goblin – Hunter (the one that sets traps; I have a pirated copy, so I might be mistaken about the creature's name). But does it really matter which upgrade to choose?
It definitely does. A decent number of Goblin Shamans can really hinder a hero casting spells.
Творят настолько черные дела,
Что до таких блистательных идей
Не вдруг дойдет и записной Злодей
Темный адепт клана GODS