ToE H5/HoF
Magic Guild level one
Magic Guild level one Cost Requirements Magic Guild level one
  • 2000
  • 5
  • 5
Town Level 3
Effect
Allows a visiting hero to learn the spells kept within. Keeps 3 spells of the first circle.
Magic Guild level two
Magic Guild level two Cost Requirements Magic Guild level two
  • 1000
  • 5
  • 5
  • 1
  • 1
  • 1
  • 1
Town Level 3
Magic Guild level one
Effect
An upgrade of the Magic Guild level one.
Allows a visiting hero to learn the spells kept within. Adds 3 spells of the second circle.
Magic Guild level three
Magic Guild level three Cost Requirements Magic Guild level three
  • 1000
  • 5
  • 5
  • 2
  • 2
  • 2
  • 2
Town Level 3
Magic Guild level two
Effect
An upgrade of the Magic Guild level two.
Allows a visiting hero to learn the spells kept within. Adds 3 spells of the third circle.
Magic Guild level four
Magic Guild level four Cost Requirements Magic Guild level four
  • 1000
  • 5
  • 5
  • 3
  • 3
  • 3
  • 3
Town Level 3
Magic Guild level three
Effect
An upgrade of the Magic Guild level three.
Allows a visiting hero to learn the spells kept within. Adds 2 spells of the fourth circle.
Magic Guild level five
Magic Guild level five Cost Requirements Magic Guild level five
  • 1000
  • 5
  • 5
  • 5
  • 5
  • 5
  • 5
Town Level 3
Magic Guild level four
Effect
An upgrade of the Magic Guild level four.
Allows a visiting hero to learn the spells kept within. Adds 2 spells of the fifth circle.
Avenger's Guild
Avenger's Guild Cost Requirements Avenger's Guild
  • 1000
  • 5
Town Level 9
Hunters Cabins
Effect
Supports Mark of the Avenger special ability. Allows selecting favored enemy
Avenger's Brotherhood
Avenger's Brotherhood Cost Requirements Avenger's Brotherhood
  • 2000
Town Level 9
Avenger's Guild
Effect
An upgrade of the Avenger's Guild.
Supports Mark of the Avenger special ability, increases chance to inflict critical hit to the favored enemy by +10%.
Mystic Pond
Mystic Pond Cost Requirements Mystic Pond
  • 500
  • 5
Town Level 3
Marketplace
Effect
Provides several random resources at the beginning of each week.
Sparkling Fountain
Sparkling Fountain Cost Requirements Sparkling Fountain
  • 1000
  • 10
Town Level 12
Mystic Pond
Effect
Provides +2 luck bonus for defending army.
Blooming Grove
Blooming Grove Cost Requirements Blooming Grove
  • 500
  • 5
  • 5
Town Level 3
Faerie Trees
Effect
Boosts Pixie, Sprite and Dryad growth by +4 per week
Treant Saplings
Treant Saplings Cost Requirements Treant Saplings
  • 3000
  • 10
Town Level 15
Treant Arches
Effect
Boosts Treant, Ancient Treant and Savage Treant growth by +1 per week
Daughter of Sylanna
Daughter of Sylanna Cost Requirements Daughter of Sylanna
Effect
The Daughter of Sylanna provides extra gold income (+5000 Gold per day), extra creature growth (+50%) and boosts luck of all player's heroes by +2. A Tear of Asha is required to build this structure.
Expert's Corner (by ThE_HyDrA)

Sylvan's special buildings are small but effective boosts to the town's resource demand. They are not spectacular bonuses, but then again, you get what you pay for.

At first glance, the Sparkling Fountain and the Mystic Pond may look the same, but you'll see that the water on the latter flows with greater fervour. The Sparkling Fountain is quite demanding in mercury, and also in its pre-requisites, while its gold cost is reasonable. Really only useful for sieges, and if you don't foresee any, then do not bother wasting mercury and a build turn on it. The Mystic Pond, however, is cheaper and is of global benefit, providing much needed resources at the beginning of the week. In such a resource-rich town as the Sylvan is, there should be no tentativeness in the prompt edification of this pond.

The two creature-bonus buildings are quite substantial, with one Ancient Treant offering an additional 181 HP per week, higher than any other creature bonus structure. Though its cost is quite exorbitant, and a good supply of Wood, Mercury and Sulfur will have to be collected if you'd like the Alcove/Arches and the Saplings. By contrast, the Blooming Grove is cheap and can be built early on (and should be), offering an additional 4 Sprites per week, a nice bonus for a spellcasting level 1 creature.

This information comes from the Heroes V release version (v3.0).

Thanks to Fiur and Vokial for in-game screenshots.
Thanks to sfidanza for the work on this page.
Thanks to ThE_HyDrA for creating and looking after the Heroes 5 section of Age of Heroes!