These 2 already exist as Protection from Cold and Protection from Fire.

I don't think the others are necessary because there is very little earth damage in the game and lightning avoiding the common resistances available against fire and cold is a major characteristic of that form of damage.

One other request, besides the summons I mentioned, earlier. It's sometimes overlooked, and it's not exactly what you asked for, but still:

For a Spellpack DLC, I'd really, really like to see the AI be adept at handling whatever spells you add, right from the moment it's offered. Not a week, or a month later. And I know this is difficult, because every time you give the AI extra choices to make in any given situation, you have to code all the potential points at which those choices might be useful, and what prerequisites would make it so, and go back and retrofit the old code to look at the new choices and consider them, as well. In addition to how these new choices might fit into tactical spell groups whose components feed into one another.

Which is my way of saying that yeah, I realize this isn't easy.

So please, don't add anything the AI can't use to the full extent of its capabilities.

Feral Mount- mounted units lose 50% att/def/movement

Frostbite- unit takes x damage each time it attacks

Sandspray- single-damage attack hits adjacent unit with a chance of blind

Blade Barrier- unit gets +20 dodge vs missiles, opponents take damage when they attack unit

Purifying Flame- unit loses 25% hp, gets cured of all maledicts

This:

I like this idea but why not have them actually lose control of the unit for a few turns.

Ya that would be great. Would add a ton of tactics and really make unit design count.

Windstorm - All units with over 20 Initiative lose -2 Initiative, and all units with over 24 Initiative lose and additional -1 Initiative.

Fiery Sun - All units with over 20 armor take 1 fire damage per unit per turn.

Also I'm thinking any rain spells should boost electrical damage.

My personal peeve with tactical summons is I how they don't scale. I would love the ability to summon creatures in groups based on that players maximum unit size and weapons. Here are some unique ideas for tactical summons...

Avenging Armor: Life Spell. Enchant target friendly unit and upon its death a group of ghosts units, you can only see their equipment, of the same size and with the same items is summoned for the rest of combat.

Tree of Life: Summons an immobile tree that heals an ally every turn.

Death Curse: Death Spell. Enchanted enemy unit takes 1 damage per unit per turn. Upon death a Death Demon is summoned under casters control.

Reanimate: Summons a group of skeletons with group size and weapons equal to last group of trained troops that died. Okay ya I know but I'm just brainstorming.

Summon Warg Pack: Summon a group of Wargs at caster's level with group size equal to that player's max group size.

Lightning Rod: Summons a immobile lightning rod with a ranged lightning attack.

Wall of Thorns: Summon a 3 tile adjacent line, think cleave, of immobile thorns with a weak melee attack.

Yeah, I guess they do!  I had to actually look them up in the Hiergamenon as I almost never take Mage and have never ever bothered taking that particular trait path if I do take Mage.

As far as earth and lightning damage, well that just means we need more spells that do that sort of damage!

But I was also thinking along the lines of such spells increasing resistance to any spell effect from that Elemental type of magic.  i.e.  Blast Furnace would make all water spells resist-able, i.e. Slow and Pandemonium.  

Tactical spells that are active for only one tactical turn are pretty much useless unless they are REEEEEEEEEEEEEEEALLY powerful.  Having to use an action to cast a 'meh' spell which only lasts one turn will never, ever happen.  Don't forget to make these spells ramp up with the number of shards under the player's control.  There are already existing spells which ought to use shards as power-ups but don't.  I also like the idea of using character level to power up spells so they stay somewhat relevent as the game progresses even if the appropriate shards aren't available.

While I'm at it, here are a couple of my own ideas:

Power Surge [Life2 & Fire2]: All units (firendly and enemy) gain +1 Spell Mastery and +1% Spell Damage per caster level
(+5/+5% per Life and Fire Shard) and +50% Attack for 3 turns.

Disjunction Dwemer [Water2 & Death2]: All friendly units gain +1 Spell Resist per caster level, +5 per Water and Death shard.

I've bolded the ideas I like out of this list and commented.  The others for the most part seem more like player abilities than spells.

More ideas:

Great Hail- fireball type spell for ice.  In a 5*5 spot, you get x number of hits randomly in the grid

Boiling Blood-  +init to unit, unit takes damage each turn

Cloudkill- poison gas cloud, does a good amount of poison damage and can stun enemy (strategic spell perhaps?)

Acid Blast- direct damage spell for earth

Wither- attempts to put an injury on a champion for the duration of combat (random)

Oblivion/Obliviate:  An unresistable singe target nuke. Perhaps part of Death 3 or 4.  Does 2 damage per level - and is effected by all the traits that increase damage.

Dispel Magic:  Battlefield wide dispel magic that removes all enchantments - even ones that make you immune to magic and supresses strategic enchantments.

Disarm: A temporary you lose your weapon spell..

Poison Cloud: An area affect spell that lasts for a bit on the map... causing poison damage. (Great for undead who are immune... I think?)

Explode: Cause target friendly unit to explode doing some sort of Area damage to all units around it?

Glacial Pillar: Creates a ice mound prop on an empty tile for 3 turns. That tile is impassable and the tiles around it slow enemies and deal cold damage to enemies on them.

Updraft: Target enemy unit is teleported to a random tile and takes caster's level in physical damage.

Magnetic Reach: Target unit moves 2 spaces towards caster and is stunned unless they resist.

Flameshape: Target unit loses half its armor and gains fire damage equal to half of it.

Drown: Target unit takes 3 + 1 per water shard cold damage per turn for the rest of combat.

Molten Spear: Fire spell that does 6 fire damage plus twice casters level in physical damage.

Lighting Storm: Every enemy unit has a 66% chance of being hit by lightning for lightning damage.

Gas Mines: Targets a tile or enemy unit. 4 random tiles are chosen around the target within 3 tiles. The first enemy to walk onto one of the tiles takes physical damage.

We have a lot of attack spells how about some more defensive ones.

I like this as long as it is actually immunity to the next hit and not invincibility for one turn. It could be 2 attacks though. Trading one action for another is kinda a waste of time.

Spell Barrier: Immunity to spells for 3 turns.

Ground: All units gain + 75 lightning resistance for 3 turns.

Summon a boulder that blocks Line of Sight.  Oh yeah, NM, that's not this game..

Sorry, couldn't resist.

What I want to see are spells that require some degree of coding and effects - not just simple XML stuff. I don't have specifics, but it's what I'd like to see.

The reason why the Leaders Pack DLC got such a big backlash was the perceived lack of effort on Stardock's part and after getting it on the 50% sale, I'm inclined to agree that it was not what we as a community felt was well ... fair.

The thing I would like to see the most though is the AI improving a lot with magic. It still is not very good at using spells and responding to players that use them.

I would like to see creatures designed to use a specific group of spells. When you encounter a group that includes one or more of these creatures you face an AI that excels in using a specific school of magic. You might have an Ogre Shamen that focuses on Offensive Earth Spells and another Ogre Shamen that focuses on Defensive Earth Magic.

Example: Frost Giants have a Shaman that casts water spells of ice and cold. Ogres have s Shaman of Earth Magic

Example Encounters with Ogres:

1. Encounter 1: 6 Ogres and a Shaman that focuses on Defensive Earth Magic
2. Encounter 2: 6 Ogres and a Shaman that focuses on Offensive Earth Magic
3. Encounter 3: 5 Ogres and 2 Shamans - one that focuses on Offensive Earth Magic and the other Defensive Earth Magic
4. Encounter 4: 7 Ogres with no magic users

Great idea!

New School of Magic: Charm

Charm school is focused on tactical mind control spells.  This school has 1 strategic spell (Mind Shield) and 3 to 4 tactical spells per level. All spells can be resisted. Charm spells are dispelled if the caster is slain. Charm spells do not affect creatures of animal intelligence or lower. (I.e. they do not affect animals, golems, spiders or the undead). Spells that affect several units have a casting time of 2.

Level 1:

1. Brainwash - target unit joins casters side for 1 turn (as per Frogboy)
2. Enthrall - target hero is frozen in place (range 1) (chance to resist each turn), dispelled if unit is attacked
3. Charm - targeted unit cannot not attack caster (chance to resist each turn) unless attacked by caster

Level 2:

1. Indecision - target's initiative reduced by -4 (unless resists)
2. Dispell Magic (unless resists)
3. Greater Enthrall - target hero is frozen in place (range 2) until attacked (unless resists, chance to resist each turn). Greater enthrall has a range of 2.

Level 3:

1. Charm Creature - Intelligent Enemy Unit joins casters side for 3 turns  (chance to resist each turn). Non-intelligent creatures (Golems, Spiders, Snakes) are not affected. Dragons are immune.
2. Fear - Enemy humanoid unit runs away (chance to resist each turn)
3. Mind Shield - Targeted Hero is protected from Charm Spells (strategic and tactical)
4. Mass Enthrall - target unit or hero is frozen in place (range 2) until attacked (unless resists, chance to resist each turn). Mass enthrall differs from Enthrall in that it can affect a unit of soldiers, as opposed to just single heroes.

Level 4:

1. Charm Hero - Enemy Hero joins casters side (chance to resist each turn)
2. Mass Berserker Rage - All friendly intelligent non-hero units go berserk and automatically move to attack enemy units until the end of the battle. Casting Time 2
3. Mass Indecision - Enemy army initiative reduced by -4 (unless resists). Does not affect those of animal intelligence or lower. Casting Time: 2
4. Curse - Selected enemy unit initiative reduced by -1 permanently. (unless resists) Can be cast multiple time on the same unit. Note that this spell's effect is permanent. Especially effective when cast on a hero that you expect to encounter in future battles.

Level 5:

1. Mass Fear - All humanoid enemy units run in fear (chance to resist each turn) Cost: 300 mana, Casting Time: 2
2. Insanity - Target unit unable to cast magic spells and initiative reduced by -6 (chance to resist each turn)
3. Mass Mind Shield - Friendly units are protected from Charm Spells for the duration of the battle. Casting Time: 2
4. Greater Curse: Selected enemy unit initiative reduced by -6 permanently. (unless resists). Can be cast once on any unit. Range 1.

New Magic Item: Helm of Mind Shielding protects wearer from Charm School Magic

New Potion: Love Potion - Heroes of Opposite Sex must resist magic to attack consumer of this potion. Effect lasts for 1 battle.

New Potion: Remove Curse - Removes effect of Curse and Greater Curse.

New Hero: Witch skilled in Charm magic.

New Creature Encounter: Witches Coven - Groups of 2 witches plus their mercenary troops.

1. Low Witches Coven - Max Spells Level 3 - 2 Witches accompanied by charmed mercenaries
2. High Witches Coven - Max Spells Level 4 - 2 Witches accompanied charmed mercenaries

Tactical Considerations: Witches are best dealt with at range, for they need to get close to use their magic.

New Conclave City Improvements:

1. Witches Coven (requires Conclave) - Allows Charm Magic Spell research. Attracts heroes that are witches.
2. Greater Coven (requires Witches Coven, Conclave Level 3) - City is protected by a witch hero unit.
3. High Coven (requires Greater Coven, Conclave Level 5, unique improvement) - City is protected a young dragon (and a witch from the Greater Coven). There can only be one High Coven in the world. Required for researching Remove Curse Spell.

New Quest: From the witch's lair retrieve a potion that will remove the curse of sleeping from my daughter, the princess.

Great ideas, I would suggest that you make charm hero the lvl 4 spell and charm creature the lvl 3 spell.

Reminds me of Saberhagen:

The Mindsword's verse in The Song of Swords describes its power as follows:

The Mindsword spun in the dawn's gray light

And men and demons knelt down before.

The Mindsword flashed in the midday bright

Gods joined the dance, and the march to war.

It spun in the twilight dim as well

And gods and men marched off to hell.

Not really a fan of new schools:

a )  The origins of this game is Elemental and I think that the idea that magic is tied to elemental forces is important to lore/feel.

b )  Gameplay-wise, I don't really like the idea of deluding the shards any further with more varieties, and I don't like the idea of a school of magic not tied to shards.

One tactical spell I would like to see is:

Downpour (Water) - Units further than 5 tiles from a player's unit are hidden from view and may not be targeted by ranged attacks. This spell would force both side (Player and AI) into martial combat, as opposed to ranged combat. It would also allow both sides to be surprised as they would not know where the enemy is concentrating their forces until battle is joined. For each water shard the range is reduced by one and the duration increased by one as the downpour is stronger and lasts for a longer time.

1 Shard: Effect Range 4+ and duration 2

2 Shard: Effect Range 3+ and duration 3

3 Shard: Effect Range 2+ and duration 4

The downside to this spell is that the AI may not react when it cannot see any units. It's units may just stand still while the enemy approaches unseen.

Heart of Darkness: This unit treats all spells with effects based on shards as if those spells depended on Death shards as opposed to their normal types.

Root: Target unit's move becomes 0 for 5 turns, and has regeneration and avoid prone in the mean time.

Magnetize: Move a unit(ally or enemy) adjacent to this unit.

Jab (Spear Skill): Attack a unit within range 2. Ignore defense.

Trap (Strategic): If an enemy unit steps on the target square, it can't move for three turns.

Release the rats: Deal 8+X damage to target unit, where x is the number of buildings in the city territory. (Not quite sure how to word that)

Hijack: Take control of another unit's spell.

I like that. I may steal it for a mod.

Generally, I want t see, make more summoning spells.

What about summoned creatures that the player does not fully control? i.e. they attack the enemy but are not controlled by the player.

1. Summon Dire Animal (Level 1) - Summons giant animal (Wolf, Bear) that automatically attacks randomly selected enemy units
2. Summoned Rage (Level 2) - Turns summoned creature into crazed berserker that automatically attacks a random unit - enemy or friendly (unless resists)
3. Greater Dire Animal Summons (Level 3) - Summons giant animal (Wolf, Bear) that is controlled by the player. (Costs more mana, higher level spell)
4. Turn Summoned (Level 4) - Selected summoned creature attacks targeted unit (unless resists)
5. Summon Dragon (Level 5) - Summons dragon to the battle. If the caster is slain the dragon becomes AI controlled, attacking friend and foe. Impressive spell, but expensive and risky.

How about Sovereign specific spells?

For example Oracle Ceresa at level 12 can summon a death demon.

Another spell ideas would be.

Elemental Binding:(Strategic or tactical) basically the tame beast spell but works on twisted and elemental creatures. Each creature has a mana upkeep of 10 or more depending on the creature tamed, with higher level creatures needing more mana. If mana runs out they become free and can turn on the player if they are near cities. But as long as mana "stockpiles" are full they will remain under player control. Sovereign should be level 8 at minimum.

I was just thinking about something similar.  Kind of like the Wild Mages in DnD, with a Summoner spin.  You would perhaps have a spell to Summon Bear, except maybe 20% of the time you would accidentally get a Berserked Dire Bear that just Rampages.  Set the Summoning range to 1 so that any summoned unit is cast adjacent to the caster.

There's potential to work something into a full Path