The Devil You Know

To get this quest flag and be eligible for Tower of Despair raid, you have to beat 4 Devil Battlefield quests.
 * A New Invasion
 * Bastion of Power
 * Genesis Point
 * Sins of Attrition

The Weapons Shipment and Wrath of the Flame are not required.

Also, Boots of Anchoring are not required to get into the raid. However, in the last fight of the raid against Horoth, players will be required to be wearing the boots, in order to avoid being subject to the Banishment spell, and be sent back to Eberron, thus ending the raid prematurely for such careless souls.

Note that in order to enter the raid, you must first cross the Devil Battlefield wilderness area (inaccessible to raid groups) to the Tower of Despair cave (where the actual raid entrance is located). There, you will find an NPC who will upgrade your Amrath portal, allowing you to return directly to the caves from Amrath.