Some ideas for new spells (level depending on the strength of the effect).
a. Acid rain, Tactical, Fire&Water: units in a certain area get x damage and have their armor reduced by % until the end of combat
b. Holy Purpose, Strategic, Life: All friendly units are filled with holy purpose: those within your Kingdom borders receive ++ damage and resistence rolls, and those outside your Kingdom borders receive + damage and resistance rolls
c. Excruciating Pain, Tactical, Death: target enemy unit receives x damage; until the end of battle, whenever this unit receives damage this is increased by %. This additional damage is illusory and is healed at the end of the battle if the unit survives
d. Water of Heaven, Strategic or City, Life and Water: City fountains spill waters that comes from the heaven. Friendly units garrisoned in cities you own heal at +200% rate and have +% life and def when fighting in a city you own
e. Eternal soldiers, Strategic, Death: whenever one of your units is killed in a battle but you win the battle, a zombie unit is summoned in its place - you can make this tactical and have the zombie raise during the battle, but die once the battle is over
f. Reaper's concession, Tactical, Death: during this battle, your units die only when their health reaches -20%. At the end of the battle, all units with negative health are destroyed.
g. Impervious Skin, Enchantment, Earth: the unit skin becomes as hard as steel: all non-magic damage is decreased by %. Any further damage reduction bonus from worn armor is not applied.
h. Call Lightning, Tactical, Air: Stormy coulds gather above the battlefield. Every turn 1-2 random enemy units are striken by a lightningbolt dealing x air damage
i. Choking smoke, Tactical, Fire: summons a smoke cloud on target space(s). Units within the cloud cannot use ranged attacks and must resist every turn or skip their turn. Units within the cloud also receive % less damage from ranged attacks.
j. Depression, Tactical, Death: all enemy units receive -x attack unit the end of the battle. When this spell is cast, any active Inspiration spell have a % chance to be dispelled
k. Inspiration, Tactical, Life: all friendly units receive +x defence until the end of the battle. When this spell is cast, any active Depression spell have a % chance to be dispelled
l. Whispering Wind, Strategic, Air: the wind whispers in the ears of your champions, revaling things seen far away; all your champions have their sight range increased by x;
m. Pathfinding, Enchantment, Earth: target unit and all units in its stack do not receive movement penalties from terrain tiles
n. Guardian Winter, Strategic, Water: A winter storm hails within the borders of your territory;
o. Ambush, Strategic, Earth: target a friendly army on the world map; if this unit attack this turn an opposing army outside a city, your units receive a % bonus to their initiative in the first round of combat
p. Frostbite, Tactical, Water: all enemy units on the battlefield receive damage and their attack speed is reduced by x until the end of battle
q. Blessing of Soil, City, Water: city crop yields increases; target city growth rate is improved by x; any Famine spell on the city is dispelled.
r. Famine, City, Death: famine spreads in the city; population drops by x, and city growth rate is decreased by y; if target city has an active Blessing of Soil spell, either Famine or Blessing of Soilare dispelled with a 50% chance. (Famine could spread to friendly cities connected with the one infected).
s. Elemental Ward, City, any element: target city have a % chance to resist enemy spells targeting the city from the opposite element (e.g. Air Ward is an Earth spell that protects against Air, et cetera); all opposite element spells cast during a tactical battle in this city have a % chance to fizzle.
t. Inquisition, Strategic, Life: while this spell is active, you are not allowed to research magic, and all spells that you and your champions cast cost twice as much mana. In all your cities non-magic research is increased by x% and unit production is increased by y%.
u. Bone Guardians, Strategic, Death: if one of your city is attacked and there are less than 8 units defending it, skeletal berserkers units are instantly summoned in the city to make a total of 8 defending units. For every two skeletal berserker units, a skeletal mages unit is also summoned. These units die once the battle ends.
v. Master of Winds, Strategic, Air: all flying units you control have their movement increased by x, and all flying enemy units have their movement reduced by y
w. Lust, City, Fire: citizen in target city are enflamed with fevering passion; growth rate in the city is increased by x, while research and production are decresed by y.
x. Poisonous water, City, Death and Water: city population decreases by x; growth rate decreases by y. Units stationed in the city do not heal and lose % health each turn.
y. Dispel, Universal, Basic; Attempts to dispel enemy spells from target unit/city; the base probability of dispelling is 50% and is affected by the number of shards you and your enemy sovreign control, the level of the spell to be dispelled, your mastery in the spell's opposite element (if you are Archmage in Light you are better at dispelling Death magic spells), whether the target is in your or his territory, and whether your sovreign or his sovreign are in that city/army.
z. Divine Shield, Enchantment, Earth and Light: target unit is immune to magic
Final comment: I have never played E:WoM so I am not sure if all of the effects listed here make sense...