Kael, some suggestions for the 'pedia.
The Mercurians <Tag>TXT_KEY_CIV_MERCURIANS_PEDIA</Tag>
The current 'pedia entry for the Mercurians consists solely of lore. It might help -- particularly newer players -- if there were some description of how the civ plays in the game, maybe adapting some of the text from the Mercurian Gate 'pedia entry. Here's some suggested text:
"The Mercurians are not available at the start of the game, but enter when another civilization builds the Mercurian Gate world wonder. The Mercurians will take over the city with the Mercurian Gate in it and become a permanent ally and teammate of the civilization that built the Mercurian Gate. A human player having built the Mercurian Gate will be given the option of abandoning the player's original civilization and playing as the Mercurians instead.
"In addition to units that they can build normally, the Mercurians gain Angels whenever a unit of Good alignment (i.e., a unit whose religion is The Order, The Empyrean, or the Runes of Kilmorph) is killed."
I don't know if that's entirely accurate, as I've never played as the Mercurians. If you accept the text, modify as you see fit.
The Hall of Mirrors
There's no 'pedia entry yet for the Hall of Mirrors, as you know. Pending the writing of a complete entry, it might help for now if there were simply a sentence or two explaining what this building does. Something like the following:
"The Hall of Mirrors creates Illusion duplicates of attacking units."
Asylum <Tag>TXT_KEY_BUILDING_ASYLUM_PEDIA</Tag>
I would recommend adding a single sentence to the Asylum 'pedia entry, something like the following:
"Living units built in a city with an Asylum have a X% chance of starting with the Enraged promotion."
I don't remember if it's Enraged or Crazed, and obviously I don't know the percentage, but this is an important side effect that should be mentioned in the 'pedia.
Council of Esus <Tag>TXT_KEY_RELIGION_COUNCIL_OF_ESUS_PEDIA</Tag>
The last sentence of the Council of Esus 'pedia entry reads "State Religion allows access to the Shadowrider unit." In the interests of being consistent with 'pedia entries for the other religions, I would recommend adding Gibbon Goetia to that sentence.
Dwarven Vault <Tag>TXT_KEY_BUILDING_DWARVEN_VAULT_PEDIA</Tag>
I know you added information in the Dwarven Vault 'pedia entry about the increased happiness and production provided by each level of Dwarven Vault. I thought the Dwarven Vaults also provided increased Great Person Points, no? If so, I would suggest adding information about that to the 'pedia entry as well.
That's all I've got for now. Hope it's helpful.