Edited Intro to this multidomain idea of mine:
The symbiosis of the darklegion and the sylvan signifies the tainting of nature's forces. This multidomain would feature creatures from one's nightmares specifically those of beasts lurking in dark forests and swamps. Vampires and goblins and other unholy beings.




To me, vampires make the most sense being a mix between sylvan and darklegion.

Duchess of Dunmelar
(vampire form)
Creature Elf Undead
1 Sylvan 1 DL 1 X 6 flux
foreststride
Blooddrain(for every 2 damage dealt by this creature, this creature gains 1 health)
Unholy(this creature is unholy and cannot be ascented)
3 attack 9 Health 4 speed 3 vision 0 range
Once per round this creature may switch forms (dims them).
Whenever Duchess of Dunmelar attacks a non undead creature that is destroyed on the same round, a "vampire" is spawned on the destroyed creature's location instead of a corpse.

Duchess of Dunmelar
(Bat form)
Unholy (this creature is unholy and cannot be ascented)
4 attack 8 health 5 speed 0 vision 0 range
Aloft
BloodLust(vampires in bat form only. All creatures within speed range is revealed.)
BloodDrain(for every 2 damage dealt by this creature, this creature gains 1 health)

Duchess of Dunmelar
(wolf form)
Unholy (this creature is unholy and cannot be ascented)
5 attack 6 health 6 speed 3 vision 0 range
BloodScent5 (all creatures within 5 spaces with less than maximum health or have max health equal to 1 are revealed).

"We had all thought she died that night. But not even the Duke could explain how she returned to us...

Vampire <--- what is spawned when the duchess damages a creature that is destroyed on the same round... also like a zombie or a sapling could be a normal card as well.
Once per round vampire can change forms. (dims it)
foreststride
1 sylvan 1 darklegion 3 flux
1 attack 5 health 3 speed 2 vision 0 range
unholy (can't be ascented or healed by holy spells)
if a creature damaged by this creature is destroyed on the same round, the creature turns into a vampire without leaving a corpse. (only in vampire form)

bat form
2 attack 4 health 4 speed 0 vision 0 range
unholy (can't be ascented or healed by holy spells)
aloft
bloodlust (all creatures within speed range is revealed)
Blooddrain (for every 2 damage dealt to a creature by this creature, this creature gains 1 health rounded down)

Wolf form
3 attack 2 health 5 speed 3 vision 0 range
unholy (can't be ascented or healed by holy spells)

Just to clarify, both the duchess and the normal vampires can only turn creatures into vampires in the low damage forestwalk vampire form, and the target creature has to be non elemental, non construct, and non undead.

I will post more on vampires, I'm going to go work on other factions' multidomains now...

Also I believe that while vampires might sound a bit cheap if you read what I made them into, please consider that they all start out in their vampire form with low damage and poor vision (except maybe the duchess but she's late game). Also to turn into the high damage high speed wolf form it would take a full round for them to change forms, or the same thing for the bat form. So it's a really slow strategy and would not unbalance the game. Also they are all 2 domain or more as they are multidomain, so they will take a while to get out.

Haunted Abode
Building base
7 flux
fear 0
0 attack 4 HP, 1 vision, 0 range
pay 1 flux, this building gives 1 domain in either sylvan or darklegion until end of round.


OR

Haunting
Enchant Building
1 darklegion 1 sylvan 3 flux
Target building base can no longer build units normally.

I like the idea but i think they are way too cheap.

Vampire must be at least 4 flux if not 5 (remember it can give you a new creature at no cost)

Duchess of Dulenmalar is a 3/ 9/ 4/ 3/ 0 and cost only 6? And 2 domains

Blunderbuss Squad is a 2/7/2/3/2 and cost 5 with no other abilities as the mighty ablities of the Duchess. Duchess must be at least 3 Domains units 1DL 1S 1X and 6 flux or maybe even 7.

duchess is 3 domains 1 Sylvan 1 DL 1 X