Enemy models in base contact with the Great Unclean One at the start of any close combat phase suffer a Wound on the roll of a 5+ which Ignores Armour Saves. This has no effect on Daemons of Nurgle.
Source: Warhammer Armies Project: Unofficial 9th Edition (v2.2)
Enemy models in base contact with the Great Unclean One at the start of any close combat phase suffer a Wound on the roll of a 5+ which Ignores Armour Saves. This has no effect on Daemons of Nurgle.