This is a very popular setup and can often be scary at times. The Warlock should use a Felhunter. There are two different ways to start against this setup. You can push for the game to start and be able to take position or you can wait and let them start. I play a Human Warlock and have the advantage of being able to play aggressively and force teams into play or bad positions at the start. You can do this by sending the Felhunter in to purge and then pull back or dotting targets.

Game Started: The Rogue will normally start and stick on the Warlock for the majority of the game. The Warlock should put the Mage as focus and stick his Felhunter on the Mage. The pet can provide push back and it will stay with the Mage. If the Mage is going to sheep something the Felhunter will be able to maintain line of sight of the target the Mage is sheeping. Your pet should be off autodevour and the Warlock needs to be very quick on devouring sheeps.

The whole objective of this game is to protect the Warlock and outlast. You protect your Warrior by keeping him mobile with devours and he will protect you with Imp Hamstrings and Intercept stuns. The Warrior will be on the Rogue for most of the game attempting to give the Warlock room to kite and stay mobile. The Warlock should DoT everything. The Warlock should be using Spell Locks on the Mage. The burst damage of this team is stupid and a Warlock can die in one stun lock. The Spell Lock on the Mage constantly should give relief to the Druid. You don't want to use the Spell Lock as a flat silence, but rather as a tree lockout. It doesn't matter if you hit a sheep or a frost bolt as long as you hit a spell. Water Elementals NEED to die. You should DoT and the Warrior should switch. The Water buddy is a huge asset to the Mage and will reduce his damage a lot if you kill it.

You can stay mobile by by receiving Abolish Poison and Warrior support. Keep in mind you are probably going to be purged a lot. It will help a ton to reapply Fel Armor when it gets purged. You should only attempt to Fear when you proc a half cast or the Rogue is CC'd, otherwise it is better if you keep moving and reapply DoTs. Deathcoil should normally be used on the Rogue and it is a good idea to use it early so it will become available again. I can't really teach you how to know when you trinket, but it will come with time. You will know when you need to move or are in danger of dying if you don't trinket. Most of the time it is when the Mage is chain casting and you can't interrupt while Rogue is on you and you're eating a full Kidney Shot, so essentially when you are stuck in the open and taking a lot of damage, use your trinket.

Now lets take a look at the Druid point of view. The Druid needs to keep a focus on the Priest as it will be his responsibility not to get Mana Burned. You can't afford to waste a Spell Lock on a Priest most of the time. You can't let a Priest Fear you. The Warrior can help with this by tossing a hamstring on the Priest when he finds time. You need to form kite patterns to maintain range and LoS of the Priest. The Druid and the Warlock need to develop a sort of synergy with kiting. They need to move as one and use the whole map. The objective is that Wounding Poison will drop and the Warlock will be much easier to heal if their isn't constant damage being pumped into him. Warrior damage and DoTs should be able to put on enough damage to the point where you will start to wear the other teams mana down. The Druid really doesn't CC that often. The Druid will Entangle the Rogue when he finds time or toss a Cyclone out to the Rogue when the Warrior can't be on the Rogue.

Eventually you will wear the other team down and any target will become viable to finish the game.