Each Chaos Mutation or Power can only be chosen once per army. Note that Daemonblade, Collar of Khorne and Chaos Familiar are also magic items, and so follow all the normal rules for items of their types (with the exception that they are purchased differently in the Warriors of Chaos army list).
Magic Weapons
The wielder of a Daemonblade has the Random Attacks (D6+3) special rule. However, every To Hit roll of a 1 made by this character in close combat is resolved against himself; the character can never re-roll a To Hit roll of a 1.
Daemon of Khorne or model with Mark of Khorne only. The character has the Magic Resistance (3) special rule.
Arcane Items
The character adds +1 to all of his channelling attempts and knows one extra spell than normal for his level.
Abilities
Instead of striking normally, the character can choose to make a single special Attack. If he does so, and the Attack hits, the hit is resolved at double the character's Strength and has the Multiple Wounds (D3) special rule.
The character has a Strength 4 Breath Weapon that has the Flaming Attacks special rule.
The character has the Scaly Skin (5+) special rule.
Daemon of Slaanesh or model with Mark of Slaanesh only. Any opponent wishing to strike the character in close combat must first pass a Leadership test (test immediately before the model rolls To Hit). If the test is failed, that model cannot make any close combat attacks that phase. This does not affect Attacks that do not roll To Hit.
The character has the Poisoned Attacks special rule and a 5+ ward save against Poisoned Attacks.
Whenever this character suffers an unsaved Wound in close combat, the model that inflicted that hit must pass an Initiative test or suffer a Strength 4 hit. Wounds inflicted by Acid Ichor count towards the combat result.
The character has the Flaming Attacks special rule and a 5+ ward save against Flaming Attacks.
Daemon of Nurgle or model with Mark of Nurgle only. At the start of every Magic phase, every enemy model in base contact with the character suffers a single Strength 1 hit, with no armour saves allowed.
Roll a D6 for each unsaved Wound inflicted by the character in close combat. For each result of a 6 rolled, he immediately regains a single lost Wound.
Daemon of Tzeentch or model with Mark of Tzeentch only. The character re-rolls ward save results of 1.
The character has the Fear special rule. However, other models can never use this character's Leadership.