We really can do better to 'reverse' Thalia, can't we?

Nonzombie creatures cost an additional to cast?

You could, and that would be a valid design, but my design was focusing on the idea that the hero completely loses her identity in death. It doesn't have to be Thalia, but I wanted to choose an established Innistrad hero, and Mikaeus was already taken.

I don't know if using a character's death to convey this sort of design would be worth it in the real-world limits of R&D, but I think it's at least interesting to explore.

I really liked the concept of the card (flavor text sells it perfectly), but I agree that it isn't really a printable design for WotC. I feel that if you wanted this to be printable, transform would be a good place to go.

Thalia, the Last Guardian
Legendary Creature - Human Soldier
First Strike
Other White creatures you control get +1/+1.
When you control no other creatures, transform Thalia, the Last Guardian.
2/1
It was Thalia's intervention that broke the siege of Thraben, and it was her death that ensured its fall.
-----------------
Thalia Lost
Legendary Creature - Zombie (:b:)
2/2
"I don't believe in heroes. In my army, a corpse is a corpse."
-Gisa Ghoulcaller

Selkie Wanderers
Creature - Merfolk Scout (R)
When Selkie Wanderers enters the battlefield, choose journey or destination.
Whenever Selkie Wanderers becomes blocked, if you chose journey, draw a card.
Whenever Selkie Wanderers deals combat damage to a player, if you chose destination, draw a card.
4/3

Eroding Golem
Artifact Creature - Golem (U)
Eroding Golem enters the battlefield with a -1/-1 counter on it for each land you control.
"It may take a little longer, but even a golem’s youth will fade with time."
-Andahg, artificer
7/7

Rogue Pentavite
Artifact Creature - Pentavite (U)
Flying
, Sacrifice Rogue Pentavite: Put a +1/+1 counter on target creature.
, Remove a +1/+1 counter from a creature you control: Return Rogue Pentavite from your graveyard to the battlefield.
1/1

Selkies are cool and so is your card but I confess I'm a bit mystified as to why they are Selkies in the first place. . .

Selkie Wanderers doesn't feel that rare to me. I think it should be smaller or draw more cards. It's a pretty cool design, I just think it would be more fun if it was stronger.

Rogue Pentavite makes my combo sense tingle. I like it.

I think Selkie Wanderers started smaller, but I felt like at 1 or 2 power, the journey ability just meant "never block this." Maybe it would be better as a 3/3 for or .

The rarity is for complexity reasons, just because that template isn't found on many Magic cards.

Eroding Golem is neat, although I would flavor it more towards advances in technology, personally.

I like the all the decision made on selkie as a whole.

Birthing Furnace
Land (R)
: Add to your mana pool for each +1/+1 counter on Birthing Furnace.
: Until end of turn, Birthing Furnace becomes a 1/1 Slith creature.
Whenever Birthing Furnace deals combat damage to a player, put a +1/+1 counter on it.

Paradise Aerie
Land (R)
: Add to your mana pool.
, , Sacrifice Paradise Aerie: Put a 0/1 green Bird creature token onto the battlefield. It has flying and ": Add one mana of any color to your mana pool."

Lionheart Paladin
Creature - Human Knight (R)
First strike, vigilance
As long as you have less life than an opponent, Lionheart Paladin has indestructible.
"Death can wait."
2/2

I don't like how slow Birthing Furnace is, but the others are pretty cool.

I was about to make a new "Random Cards from Jim" thread, but apparently I already have one.

Blade of the Fates
Artifact (U)
If a card would be put on the bottom of your library from anywhere, put that card into your graveyard instead.
, : Scry 1.
Miranus saw all his possible futures laid out before him like tiny strings, ready to be cut.

Despite its CotW popularity, I think the amount of interesting design space in Compromise is pretty small. Anyway, here are my attempts to find designs for colors I haven't done yet.

For Glory
Instant (U)
Creatures you control get +2/+1 until end of turn.
Compromise (You may cast this spell for its compromise cost. If you do, each opponent copies it.)

Mutual Hate
Instant (U)
Creatures you control get +2/+0 until end of turn.
Compromise (You may cast this spell for its compromise cost. If you do, each opponent copies it.)

Collaborative Research
Instant (U)
Draw two cards.
Compromise (You may cast this spell for its compromise cost. If you do, each opponent copies it.)

Thunder Dance
Instant (U)
Thunder Dance deals 3 damage to target creature or player.
Compromise (You may cast this spell for its compromise cost. If you do, each opponent copies it and may choose new targets for the copy.)

Ironically, white is the worst color at compromising, just because it doesn't have a lot of spell effects that benefit from a cost reduction. I tried to make it work, but ultimately I liked the Trumpet Blast version better than the Inspired Charge one.

I feel like white compromise cards would wind up with a lot of lifegain or token generation. Although, on the other hand, one of white's flaws is zealotry, so it could also potentially just be the most uncompromising color.

Somewhat inspired by Mana Tide Totem.

Hunted Informant
Creature - Human Advisor (R)
At the beginning of your end step, draw a card.
Hunted Informant blocks each turn if able.
"Treason will not be tolerated in the high city."
-Queen Marchesa
0/2

Edit: Tweaked flavor text.

i love jam.
i love jim.

Jammin

Layered Jelly
Creature - Ooze (R)
: Layered Jelly gets +1/+1 until end of turn. Activate this ability only once each turn.
: Change Layered Jelly's base power and toughness to its power and toughness. (This effect lasts indefinitely.)
1/1

The constant keeping track of new base power/toughness after a weird buff (something like +2/+4) spells will be kinda a hassle. And I felt like "buff spells become permanent" is kinda a common design troupe.

"T: put a +1/+1 counter on this" was too simple for you?