Sorry, can't find the thread either, but I'll give you the gist on the dusty ones.
Basics
Magic: Other than characters and one or two spells the Tomb Kings have little Magic
Chaff: If facing sphinxes, get the extra Host. If not, get bats and wolves
Marching: For some reason, Games Workshop left a March-enabler out of the Tomb Kings army, so use this to try to outmanoeuvre them
Hexwraiths: They could work, but drop the Champion, because Hexwraiths close combat against Tomb Kings means they'll crumble. Also, watch that the Tomb Kings Lore Attribute (The Restless Dead) grants D3+1 WOunds to an augmented unit This means a) they will not need to cast an additional spell, and can regenerate a unit and buff (or move, Signature spell gives 8 inch movement) and heal in same casting and b) 5 Hexwraiths will likely casue only 4 or five Wounds on a unit, which would be easily healed (though the cavalry units are smaller, and can be engaged by Hexwraiths).
Sphinxes: While high Toughness and 5+ Armour, with -1 to crumbling, Sphinxes can only heal 1 wound per phase (or casting? Forgot) and have no Magic, meaning they can either be tied up by Hexwraiths, meaning they'll need to divert another unit/spell to deal with it, which will take a while with no Marching, or attack it and be confident that you'll hurt it faster than they can heal
Now, the Tomb Kings
Characters
Because of how Tomb Kings characters operate, it is even more important to target them than other characters.
Tomb Kings: These are the generic Lord characters, with and almost identical Hero version called Tomb Princes, different only because of -1 Weapon Skill and -1 Strength on The Curse (causes damage to the model/unit that killed it).
They have a rule called My Will be Done, which grants their Weapon Skill to a unit they are in (not mounts). This means that one or two Tomb King units will have WS 6/7, without magic. However, apart from 1 more Wound, they have identical Weapon Skill, an dan otherwise worse profle (including unusually low Leadership for a combat character).
Liche Priests: Lord High Liche Priests, Hero Liche Priest. Generic casters. Light, Death, or Nehekhara. One must be Hierophant. Grants Regeneration (6+) to unit. However, must take Lore of Nehekhara (weakest of the Lore choices they have) and if dies army crumbles. Like us, but no back up caster ability. Home in on, and win.
Necrotects: Architects locked up and sacrificed after building pyramids. Now back with a fury at their constructs being destroyed. Give Hatred to unit and Regeneration(6+) to Animated Constructs (Sphinxes and statues) within 12 inches. Kill to weaken animated construct units, and removed combat ability from units.
Core
Skeleton Warriors: Exactly the same as ours, but will be taken more often as no Zombies. Zombies chaff these well, as same role but cheaper.
Skeleton Archers: Arhcers that use arrows blessed by the asp goddess to never miss (in theory...). Bows. Arrows of Asaph means they never modify their BS due to cover, etc, to balance BS 2 to some extent. All bow units have this. Because no modifiers affect their shooting, cover and distance are useless against them (except 48 inch Gaze). Close as quickly as possible.
Chariots: Chariots, riders are hit on one die score lower than normal. Can be joined by chariot-riding Tomb Kings and Tomb Princes for My Will be Done. Have bows and spears, with two riders (character replaces one). Can be fielded in units. Destroy with Hexwraiths.
Special
Tomb Guard: Partially mummified Royal Guard. Like Grave Guard, but magic hand weapons, or flails. Chaff up.
Ushabti: Statues that replace the chosen of the gods.
Animated Constructs. Expensive. Great Weapons or S6 bows. Chaff up.
Tomb Swarms: The husks and shells of vicious creatures of the desert infesting the Necropolis. Poisoned Swarms. Never considered them, so can't really comment.
Necrosphinx: I think it's a giant statue of a cat. Can have breath weapon or poison. Spirit Host will do the job nicely.
Rare
Probably won't be used due to points restrictions, but stronger sphinx and monster that grants extra power/dispel dice.
Your army
Necromancer: Disepl Scroll. I would advise against paying for a 6+ save. Get an extra Zombie or two.
Core
Zombies: Good against Tomb Kings, as they chaff their units for cheaper than their chaff. You'll need to really take advantage of The Newly Dead here.
Special
Hexwraiths: Use then to run through units with characters, especially the Hierophant.
Hopefully that helps.
By the way, there used to be an Army Specific Tactics forum here. Where did it go?