Keli'dan the Breaker Abilities

1. Burning Nova is an AoE dealing 5,000 damage, you will know when this is coming because of the emote Closer! Come closer... and burn!. Everyone should run to the outer wall, even the tank, ranged stay max distance and run as well.
2. Shadow Bolt Volley is thrown at all party members, dealing 1,000 damage each.

Keli'dan the Breaker Strategy

1. When you enter Keli'dan's room you will be faced with 5 warlocks, these can be crowd controlled and killed down one at a time. They will put a nasty debuff on the party called Mark of Shadow, this needs to be dispelled or cleansed. If Mark of Shadow is not cleansed it will increase shadow damage by 1,100. Once they are dead the boss will engage.
2. The real thing to watch out for with Keli'dan is his Burning Nova. You must run very far away, you can easily die if you are caught in it. When Burning Nova is fully avoided, Shadow Bolt Volley will be thrown at everyone.