Instances

Instances are areas independent from the rest of the world. What this means is that you have to go through a loading zone first to enter it, and every instance is independently loaded. So for example if you have two groups of five people and they both enter Ragefire Chasm at the same time, they'll end up in different instances of the same.. instance. Get it? If you ever played Anarchy Online or City of Heroes this is easy to understand. Instances have quests that are usually marked with (Elite) on the end of the quest name because instances have Elite monsters.

Elite monsters have huge amounts of HP and more resists, as well as more damage. Generally an elite monster is better than one of the same type two levels above it. They also drop better items and more money. This makes instances primarily for grouping.

Instance bosses are also elite.. and a pain in the ass. You need a good group of decent level to do instances. But a really good group can do them at low levels as well.

So let's use Ragefirm Chasm as an example, the first instance you can really use as Horde. It's for levels 13-18. If the group was all level 13, you would probably die within the first 5 minutes. If you were all 18, it'd be too easy. But a group with a 16 warrior, a 14 priest, 14 mage, 15 rogue and a 13 warlock could probably do it. It depends.

Note that instances drop loot that is usually geared for the minimum level I listed. Farming RFC at level 20 won't help your character.