When Kostaltyn is down to two Wounds, he gains the Regeneration (5+) special rule. When he is down to one Wound, he gains the Regeneration (3+) special rule. Roll each To Wound roll against Kostaltyn separately.
Source: Warhammer Armies Project: Unofficial 9th Edition (v2.2)
When Kostaltyn is down to two Wounds, he gains the Regeneration (5+) special rule. When he is down to one Wound, he gains the Regeneration (3+) special rule. Roll each To Wound roll against Kostaltyn separately.