Models with this special rule are collectively known as Chaos Champions. They can never refuse a challenge and, if possible, must always issue one. If there are several Chaos Champions involved in a combat, the controlling player chooses which will issue/accept the challenge.
In addition, if a Chaos Champion kills an opponent in a challenge, or if he kills a monster, immediately make a 2D6 roll on the Eye of the Gods Table. Once the result of the roll has been determined, make a note on your army roster – that model now has that reward for the rest of the battle. A Chaos Champion can have several rewards, and it can even have the same reward multiple times. These rewards cannot increase a characteristic above 10 or an armour save beyond 1+. If, for any reason, a reward cannot be applied, the result is instead treated as a ‘The Eye Opens’ result.
Note that the Chaos Champion must cause the last unsaved Wound on a model to claim the kill (if a model suffered multiple Wounds simultaneously, randomise between the sources to determine which caused the final Wound). Causing an Unstable enemy to perish as a result of combat resolution, or catching an enemy character/monster that flees from combat, for example, do not count.