Isiset

Isiset, the construct of magic, is a boss of the Halls of Origination in World of Warcraft: Cataclysm.

Tactics summary

Normal: During normal phase, interrupt Veil of Sky, and keep adds tanked near the boss. Face away before Supernova lands to avoid being blinded. When she splits into 3 the first time, kill Astral Rain to stop her AE ability. The second time, kill Veil of Sky to stop her shield ability.

[Supernova]—Isiset channels a supernova, causing all nearby enemies who look upon her to suffer 19500 Arcane damage and wander blindly for 4 sec.
[Astral Rain]—Summon a flurry of stars from the sky on all targets, each dealing 5000/7500/10000 Arcane damage.
[Veil of Sky]—Drapes the caster in a protective shield, absorbing up to 100000/200000/300000 damage drain mana instead of health. Also reflects 20/40/60% of magic spells.
[Celestial Call]—Summons 1/2/3 Celestial Familiar(s).

[Astral Rain]—Summon a flurry of stars from the sky on all targets, each dealing 7499 Arcane damage.

[Veil of Sky]—Drapes the caster in a protective shield, absorbing up to 100000 damage drain mana instead of health. Also reflects 20% of magic spells.

Periodically, she casts Supernova. Everyone must face away from her at cast completion, or be blinded for 3 seconds.
At 60% Isiset splits into Astral Rain, Veil of Sky, and Celestial Call. After one dies, the other two vanish and Isiset reappears. However, she will not use the ability matching the name of the mob that you killed. Additionally, the two abilities that remain are stronger.
At 30%, Isiset splits again into the two remaining abilities. After one dies, the other vanishes, and Isiset reappears. This time, she will only use the remaining ability, but it will stronger yet again.

HEROIC

We found out the best way to kill Isiset is to have her last ability be the less damaging one.
Kill her "clones" on the following order (it helps to mark the correct target when she splits:

1) Astral Rain

2) Celestial Call

3) Veil of Sky

Leaving Celestial Call for last might work but leaving Astral Rain for last will most likely lead to a wipe due to the huge amount of damage, so always leave Veil of Sky for Last.

Normal Mode
Legwraps of Astral Rain Item Level 333 Binds when picked up Cloth Legs 1002 Armor +268 Intellect +401 Stamina Durability 100 / 100 Requires level 83 Equip: Improves critical strike rating by 178. Equip: Increases your mastery rating by 178. Sell Price: 9 99 9 Ring of Blinding Stars Item Level 333 Binds when picked up Unique-Equipped Finger +149 Agility +224 Stamina Requires level 83 Equip: Improves haste rating by 100. Equip: Increases your mastery rating by 100. Sell Price: 5 34 34 Armguards of Unearthly Light Item Level 333 Binds when picked up Plate Wrist 1369 Armor +114 Strength +224 Stamina Durability 45 / 45 Requires level 83 Equip: Increases your dodge rating by 149. Equip: Improves hit rating by 76. Sell Price: 8 76 8 Nova Band Item Level 333 Binds when picked up Unique-Equipped Finger +149 Strength +224 Stamina Requires level 83 Equip: Improves critical strike rating by 100. Equip: Improves hit rating by 100. Sell Price: 5 34 34 Blood of Isiset Item Level 333 Binds when picked up Unique-Equipped Trinket Requires level 83 Equip: Increases your mastery rating by 252. Equip: Your healing spells have a chance to grant 1512 Spirit for 20 sec. Sell Price: 8 5 7