Freeze and Tremor without a doubt! AI should really use these more often as it can really hurt the player wandering in enemy territory.

Edit: pillar of flame is pretty good too.

Wither can be devastating with enough death shards. And since death shards can be converted from other shards by a spell..

IIRC -2 attack per shard, no save when cast on strategic. Let's say 6 shards, convert all to death. That's a -12 atk for each figure of a, say 6 man unit. Negligible cost.

I no longer play Ceresa since she can just walk all over the map with Wither.

Cloud-walking. It's expensive, but it really comes in handy when you want to get the job done and get experience for it, too.

My favorite is tidal wave, watching that wave come in is so fun, and it's so cheap. That and I can grab it on the way (edit: I mean grab it right after) to getting mantle of the oceans for cheaper tactical spells

Aside from that, starfall, tremor then wither.

Also, I would love to see the AI using strategic spells on me (beyond city based ones).... just sayin

I don't use offensive strategical spells much but I do love me some unit buffs, city enchantments and cloud walk. Makes me think back to Master of Magic when you could make godlike units with buffs (like fully buffed War Trolls). Stuffing your sovereign with buffs makes Procipinee's Crown so worth the point.

As all stated above and Nature's Bounty/Gentle Rain to help speed my Fortresses to Strike Garrison (and first strike Archers of Win).  Though in LH, this strategy is not nearly as effective as it once was...

Would love to see specific Strategic Spells/Items/Buildings for different sov professions.  I really enjoyed finding a Summoner's Ring with my Summoner Sov and the Azure Collar quest netted me Thog the Fierce an Escaped Juggernaut I was able to tame.  

Orzag the Juggernaut with the Sword of the Void is a Trog, while the Escaped Juggernaut is Twisted...  is that intentional?

Strategic spells I always use:

- Meditation

- Oppression

- Pillar of Fire

- Starfall

- Wither

That's pretty much because the custom sovereign I like to use is death/fire magic and Resoln!

Also:

With steam integration you could probably track this kinda stuff now..... just sayin

Empire's Wither is a must have and will become unbalanced as soon as you control ... let's say 3 death shards.

Tremor, Freeze, Tornado and Cloud Walk are very very important on large / huge maps.

As long as the AI don't use them, these 5 spells are all unbalanced anyway.

mass spam arcane monolith... most used strategic layer spell.  Especially since you can spam it around someones borders to 'push' them back and grab their resources.

Tornado is a game-winner. No army can survive being completely separated then defeated one at a time. If you have 5+ air shards it also does good damage, making it downright unfair. On top of all that, you can cast it outside your territory.

Mantle Of Oceans is almost as powerful if you've been cultivating mage champions. 

Sacrifice at Death 5 is really useful in a pinch.