Tomb Kings have 3 consensus playstyles that have proven to be fairly successful, all of which I have christened with nicknames:
1. Come Get Some. This style relies on a shooting and offensive magic-heavy backfield to force people to come to them as they take casualties, then a couple of beefy units to crash into them and finish the job. Usually, that backfield will consist of a LOT of Skeleton Archers, a Casket of Souls, and 2 Screaming Skull Catapults, with Tomb Guard, Ushabti, and Warsphinxes waiting for any potential enemies to get close.
2. Death from the Sky. This list employs Khalida (a special character) who greatly enhances the abilities of Skeleton Archers as a kill mechanism. With her in the unit, a TK Skeleton Archer always hits on a 4+ (as opposed to a 5+ by default), and all his shots are Poisoned. Combine that with Righteous Smiting (a spell in the TK Lore that gives a unit Multiple Shot (2)), and you can potentially delete entire units in a single turn. She's typically fielded in a giant block of 60+ Archers, with Sphinxes and other tough roadblock units to engage and hold up anything coming at them that isn't being shot at.
3. Fast and Furious. This list employs units with large Movement values (such as Necropolis Knights and Chariots) along with a formidable magic engine (2 L4s with Hierotitan and Casket of Souls for extra power dice, extra bonuses to casting value, and a huge spell selection) to make for a fast-moving MMU style list that seeks to apply overwhelming force in a precise spot.
The one common thread here is that TK like having lots of magic, so the Casket of Souls and even the Hierotitan are fairly popular choices.
