This is large pack of suggestions or one big suggestion depending how you want to see it and may require a lot of work and tweaking and only just because of that it might not be valid
Also this suggestion is little different and may break some rules of the competition but I put a lot of thought and creativity into this and I want to share this with you all.
The base of this promotion is the same but all the nations get their own version of it. The names are from real life science but I think they fit really nice in here.
The base of this promotion is the Academy building founded by a great sage.
Once you build Academy to a city, that city will act as the base of the promotion.
Some of them give permanent promotion to units built in that city while others give temporary promotion to units stationed in that city.
The promotion itself goes by the titles below and is visible in units promotion list as long as the conditions are met to keep the promotion.
If the academy and/or the city is lost then the promotions should vanish or stop working too because not all nations have permanent promotion type.
Some of them are fairly compact and clean but some require a lot of explaining and Ive been putting
Italic to parts that should not end up visible to player.
Ive been also making extra notes to make the purpose of them more clear.
For example there is
Restricted: which means that those units cannot get the promotion. There is also
Doesnt work with: which is essential to remember to prevent any contradictions (for example: sacrificing units in city to produce golems).
I also added minor backfires to some bonuses to balance the promotions and make them more fun and exciting. But still, these promotions was meant to be minor, not gamebreaking. Also I havent decided yet should I restrict the number of these "advanced academies" but I think 1 is not enough and 5 is too much so lets stick with 3 for now.
Sorry for long post heres the promotions
Oceanology
the study of oceans Lanun
Naval units built in this city get +1 movement and +1 sight range in ocean tiles.
Restricted:
hero units
national units
Heliology
the study of the Sun Malakim
Units built in this city negate 1 first strike from foe and get +2 first strikes against hidden enemies.
Restricted:
hero units
Hematology
the study of blood Calabim
Vampiric units built in this city will heal +5% after defeating living unit and +5% while moving.
Restricted:
hero units
Enigmatology
the study of puzzles Balseraphs
Has a random effect for the citys productivity depending on the number and type of units stationed in it.
[This part is not explained for the player but the academy in city screen shows these productions without the units that add them.]
+1

/ arcane unit
-1

/ archmage
+1

/ melee unit
-1

/ siege unit
+1

/ worker unit
-1

/ settler
+1

/ divine unit
-1

/ hero unit
(max 4 same class units and total max 8 positive units/city)
(max 5 same class units and total max 10 negative units/city)
[This part does not show in academy but has clues in city screen.]
+1

/ slave "Its good to own some authority."
+1

/ foreign unit "We dont trust everyone here!"
+1

/ medic unit "Herbalists are receiving help."
+1

/ wounded unit "Herbalists are too busy."
(total max 4 positive units/city)
(total max 6 negative units/city)
[This part is completely hidden.]
+1 crime rate / recon unit
-1 crime rate / archer unit
(total max 5 units combined)
Units that exceed the limit will have the promotion icon but wont contribute anything to it.
Restricted:
summoned units
Gemology
the study of gemstones and ornamental materials Luchuirp
Golem units built in this city get 20% chance of negating spell damage.
1% chance that damage will amplify 100% instead.
Doesnt work with:
world spells
Restricted:
hero units
national units
Epidemiology
the study of the origin and spread of diseases Sheaim
Units
in this city are immune to disease and spread disease to foes.
Has 1% chance per turn to mutate one unit in the tile.
Restricted:
siege units
Dragonology
the study of dragons Kuriotates
Units
in this city are immune to fear and have 15% chance of causing fear in combat.
Has 1% chance per turn to cause smoke in forest/jungle near the city
(1st - 3rd ring).
Restricted:
siege units
Biology
the study of life Elohim
Divine units built in this city will heal living units in the tile for 5% for every death
(friend or foe) that occurs 0-1 tiles away
(cap at 50% heal/turn).
Restricted:
hero units
Angelology
the study of angels Mercurians
Defeated angelic units built in this city get 10% chance to be resurrected without exp at players capital.
1% chance the resurrected unit will be unable to get exp.
Doesnt work with:
sacrifice
any mechanic that makes another unit when this one dies
Restricted:
hero units
immortal units
national units
Ethology,
the study of animal behaviour Doviello
Non-animal units built in this city get +25% chance to subdue animal outside borders and 50% chance to copy one promotion from tamed animal.
Restricted:
hero units
siege units
Dendrology
the study of trees Ljosafar
Worker units built in this city build improvements twice as fast in forest tiles.
Doesnt work with:
actions that will remove forest
Cryptology
the study of encrypting and decrypting secret messages Svartalfar
Recon units built in this city get +2 first strikes against hidden nationality units and hidden nationality units built in this city get +2 first strike against recon units.
Restricted:
hero units
Mineralogy
the study of minerals Khazad
Siege units built in this city can bombard twice from hills and do +20% collateral damage in hills.
Sociology
the study of society Bannor
In war: Military units built in this city get +15% city attack inside enemy borders.
In peace: Military units built in this city get +15% road movement inside own borders.
When vassal of stronger nation: Military units built in this city have -15% city defense
Restricted:
hero units
national units
Ontology
the study of existence Grigori
Units built in this city get resistance to magic according to number of mana spheres controlled.
1% chance unit gets permanent -10% magic resistances instead.
1 mana / 10% magic resistance.
Caps at 30% per mana type.
Same type of mana can stack.
The promotion lives with the situation so any changes to mana numbers will change the promotion aswell.
Restricted:
adventurer units
national units
Toxicology
the study of poisons Clan of Embers
Units
in this city are immune to poison and have +1 poison combat.
Restricted:
siege units
Futurology
the study of the future Amurites
Arcane units built in this city get exp faster according to number of mana spheres controlled.
1 mana / +5% exp.
Cap at +50%.
Same type of mana can stack.
Upgrade cost for these units increases.
1 mana / +10% cost.
Cap at +100%.
Same type of mana can stack.
The promotion lives with the situation so any changes to mana numbers will change the promotion aswell.
Doesnt work with:
exp gained from combat
Restricted:
hero units
Hippology
the study of horses Hippus
Mounted units
in this city have double fortification bonus and dont have restrictions for defensive bonuses.
Restricted:
hero units
Chronology
the study of time Sidar
Sidar units defeated
in this city have 15% chance to spawn a copy of the unit with same promotions and exp.
1% chance to spawn a barbarian copy to nearby tile instead.
Doesnt work with:
sacrifice
any mechanic that makes another unit when this one dies
Restricted:
hero units
summoned units
siege units
national units
immortal units
Glaciology
the study of glaciers Illians
When fortified in ice or tundra tile, units built in this city get +30% defense and heal extra +10%/turn.
Restricted:
hero units
national units
Demonology
the study of demons Infernal
Demonic units built in this city have 20% chance to explode when killed, hurting only foes.
1% chance the explosion hurts only friends.
Shares same mechanics with pyre zombies.
Restricted:
hero units
national units
Edit: fixed some grammar
balanced doviello and added copy effect
balanced illians