I think that there should be a way to dispel 'Unhoy Cataclysm'. It should be harder to dispel than most spells, but there should be a way;it could represent a wizard banishing the dead souls back to the underworld or something like that.Maybe it can only be dispelled on 35+, to represent how hard it is to deal with the restless dead. But you should still be able to dispel; this isn't some overpowered, glitchy Skaven spell, it should be a 'fair' spell.
Second of all, Usurper does not clearly state that when you resurrect a model that you kill via this spell, it becomes under your control. I think that a model trageted by Usurper should not have to be in combat with the wizard but within a 24" range of the wizard (like Fate of Bjuna and Caress of Laniph). I think that 'The Walking Dead' should be cast on 20+ as it is not 'all friendly undead within a specific range' but 'all undead on the board. Here are my suggestions for these three spells:
The Walking Dead 20+
Presence
As the power of the fulcrum invigorates that of the long dead liche, so in turn this is passed onto those around him. With terrible lurch the dead creep towards their foes faster and faster......
During the next Legion of Nagash movement phase, all Nagashi Undead on the board may make march moves as normal, following the marching rules in the rulebook.
Usurper 20+
Equilibrium
Fluff
The wizard must select one model in base to base combat. Both players roll D6 and their leadership. If the casting wizard exceeds the opponents roll, he inflicts a number of wounds equal to the amount he beat the opponents roll. These wounds cannot be save in any fashion. If the wizard does not exceed the enemies roll, nothing happens.
In addition, any models that are killed in this way are immediately turned into Undead. The model is now under your control. They retain all stats, rules, items they had, however they now also have the Undead special rule. If the model was a mount previously the wizard may choose to immediately mount the model (providing he does not have an existing mount).
In all instances place the model within a 6" radius of the wizard, this may be in contact with an enemy unit in which case the new model counts as charging in the next combat phase. If you cannot place the model due to limitations of size or rules (such as the model may not join the unit), then you may exceed the 6" radius by the least amount possible to place the model.
The Dead Shall Rise 28+
Dominance
As the fulcrum's energies flow across the field of battle the liche's, imitating their master, channel the energy into the corpses of their foes, flaying flesh from bone and raising their remains up to fight for their rightful lord.
Select one of your opponents destroyed units. Summon 1 Pinnacle Guard unit within 12" of the caster of a size equal to the total wounds of the selected unit. If the destroyed unit had command models, the raised Pinnacle Guard unit will also have these models. If one or more characters died with the unit, then a Zenith Prince will also be raised, although his three wounds will be deducted from the number of wounds used to raise the unit. If possible, the raised unit will also be equipped in the same way as the destroyed unit. If this is not possible, they will be equipped with hand weapons & heavy armour.
Also, the selected destroyed unit cannot afterwards be the target of the (insert name here - Lore of Life Cataclysm spell that can revive a destroyed unit).
Unholy Cataclysm - casts on 30+ Remains in Play
Dominance
As the Necromantic energy sweeps over the battlefield, the spirits of the long-dead join together to form a great congregation of death. As the caster gives the blood-sacrifice, the spirits run wild and sweep over the land, taking with them more souls to join their unholy cataclysm...
Once this spell has been successfully cast, it cannot be cast again, or dispelled in following magic phases. Roll a D6 for every enemy unit on the board. On a 4+, this unit takes a wound with no armour saves allowed. Make a tally of the number of wounds caused this way. In each subsequent magic phase, roll one D6 for each enemy unit PLUS the number of wounds already caused by the spell, split up as evenly as possible; a roll of a 4+ will cause a wound with no armour saves, as detailed previously. Continue to keep a tally of the number of wounds caused each magic phase, adding to the previous total each time the Unholy Cataclysm causes a wound, and adding that many dice to next magic phase's Unholy Cataclysm.
(Eg: Unholy Cataclysm is cast and causes three wounds. Next magic phase, a D6 is rolled for each enemy unit, PLUS an additional 3 D6 rolls split up as evenly as possible between each enemy unit. This causes a further four wounds, meaning next magic phase one D6 is rolled for each enemy unit PLUS an additional seven D6 split up between the enemy units (the initial three and then the next four wounds caused adding together) and so on and so on.)
Like them all. You could have four spells (not usually allowed, but oh well) or three, but at the moment, I can't decide between 'Unholy Cataclysm' and 'The Dead Shall Rise'. I like the idea of loads of guys being resurrected but I like spirits dragging souls away too. Maybe you could have some super-combination of both as the third spell. But it's up to you.