To limit the amount of C9 Gold and time spent preparing for a match; Arena’s have a number of special rules:
When you enter the arena, you are placed in a small waiting area. All buffs you had prior to entering the arena are removed, as well as conjured items and pets. (this includes summoned food and drink, which can be annoying)
While in the little prepping area, you can use buffs, summon pets and conjure items at no mana (or soul shard)cost.
Abilities with cool downs longer than 15 minutes cannot be used in the arena.
When you enter the arena, any ability with a cool down of 15 minutes or less is reset, so that you will be able to use it inside.
Terrokar Forest
The pvp in Terrokar works somewhat differently in that the objectives may only switch sides once an hour. There is a timer counting down in that zone, and when it hits zero the five towers surrounding auchindoun are free for the taking again.
Whoever gains control of all the towers first will reset the timer and gain 5% experience, 5% damage and the ability to gain Spirit Shards? See the outdoor pvp rewards sub chapter for info on those.