MTG Salvation

This concept could potentially be very flexible. You could have different card types for each mode. Even a land as one mode and another card type for the other, that would be an impressive card for sure.

Let's give that a crack, shall we?

Elven Domicile
Land
(You may play either face of this card.)
~ enters the battlefield tapped.
T: Add G to your mana pool.
-----------------------
Elven Resident 1G
Creature - Elf Citizen
2/2

So you're proposing cards with an alternate casting cost that results in an alternate version of the card, and trying to apply this to creatures.

Other than the creature part, you're essentially making a split card like Wax // Wane, which gives you a choice between two different effects that have different mana costs. Split cards are inappropriate for permanents though, due to the confusion of having them remain on the battlefield.

I think the cleanest way to implement this would be a double-faced card that allows it's owner to cast either face from the hand.

So:

Cuty Elvese GUU
Creature - Elf
Flying
(You may play either face of this card)
1/1
----------------
City Elve GWW
Creature - Elf
Trample
1/1

The front face would need a marker near the mana cost to indicate the mana cost of the reverse face, similar to the existing double-faced cards having a reminder mark near the power and toughness indicating the power and toughness of the reverse face.
It's novel twist on an old idea.

No, no one cares about humans.

I can't really see Ritual Assassin as a common, that effect is just too much of a hoser, and getting double-use out of it with the embalm is kinda overpowered.

I'm going to oppose the Exonerator too, if you want these to be commons, combining a sacrifice ability with a cheap embalm is not the way to do it, that complexity and power is too much for common.

Hazoret' Zealot really should be a Jackal, Tundra Wolves is a classic card deserving of homage.

Desert Lion and Attendant Wing are on-point for fun commons that callback to classic white 1-drops.

No, not a scanned image, write out the card in standard template.
Like this:
Eternal Witness would be:

Eternal Witness 1GG
Creature - Human Shaman
When Eternal Witness enters the battlefield, you may return target card from your graveyard to your hand.
2/1

That way I can see how you're trying to implement your mechanic, your description is too generalized. We don't need to see it in a card frame unless you're doing something with the frame that's important to the design.

WB Knights
U Merfolk
WUBRG Slivers
BRG Dragons

Good lord, that spell is unbelievably overpowered. It also breaks the game.

Phantasmal Phobian 4UB
Creature - Nightmare Illusion
~ can't block.
When ~ becomes the target of a spell or ability, sacrifice it.
When ~ enters the battlefield, exile all the cards in target opponent's hand until ~ leaves the battlefield.
5/3

I'm having a hard time understanding what you're trying to describe in that message. Can you provide an example of this mechanic on a card design?

The name is of course open to modification. Berserk might not be the best choice since the card Berserk does something completely different. I went with it mostly because two of the existing creatures Berserk Murlodont, and Elvish Berserker, used it as their theme.

(Also, jeez, that Murlodont is just a garbage card!)

I'm strongly opposed to errataing Rampage into Neo-Rampage, it dramatically changes the functionality of the old cards. There may not be many of them, and they may all be very old and bad at this point, but design takes great pains not to change old cards with new rules (other than Mana Burn of course). A new keyword for it is more appropriate.

Flanking is another potential candidate for this treatment,it would be very easy to apply a number value to flanking to expand it's design space. The issue with flanking has always been it's strange interaction with itself though. And errata for that would again change function too much I feel.
If only Bushido didn't have such a setting-specific name...

So, I always liked rampage, but it was retired long ago. An it was always unimpressive without trample, creatures simple don't get multiblocked.

However, the times have changed. Menace is now an evergreen keyword that works really well with a rampage-like ability as well as with trample.

Thus, I propose a new keyword that would fill the same space as rampage, based on the variants Wizards themselves produced in the wake of rampage's retirement.
Based on Elvish Berserker, Rabid Elephant, Spinded Sliver, Berserk Murlodont, and others.

Berserk # (This creature gets +#/+# until end of turn for each creature that blocks it.)

Simple, direct, easy to understand and use, meshes well with trample, menace, and first strike. Red and green are the obvious place to put it, but it could venture into black too.

I doubt that this is a new idea, but I think that the time is right to bring it back.

Examples:

Rabid Elephant 4G
Creature - Elephant
Berserk 2 (This creature gets +2/+2 until end of turn for each creature that blocks it.)
3/4

Elvish Berserker G
Creature - Elf Berserker
Berserk 1 (This creature gets +1/+1 until end of turn for each creature that blocks it.)
1/1

Spined Sliver RG
Creature - Sliver
Sliver creatures have Berserk 1 (Each sliver gets +1/+1 until end of turn for each creature that blocks it.)
2/2

Savage Hellion 2RR
Creature - Hellion
Menace
Berserk 3 (This creature gets +3/+3 until end of turn for each creature that blocks it.)
3/3

Skult Battlemaster 3RR
Creature - Human Barbarian Berserker
Trample, menace
Berserk 2 (This creature gets +2/+2 until end of turn for each creature that blocks it.)
3/2

Sigrid, of the Skult 2RG
Legendary Creature - Human Barbarian
Berserk X (This creature gets +X/+X until end of turn for each creature that blocks it, where X is the number of creatures that block it.)
~ Must be blocked each combat if able.
4/4

Imploding Aether 2UU
Enchantment
Whenever a player casts a creature spell, counter that spell.
0: Destroy ~. Skip your next turn. Any player may activate this abililty.

Next: Lin Sivvi, Defiant Hero

Mass Supplantation 2WU
Instant
Exile any number of target creatures you control. For each creature exiled this way, create a token that's a copy of it.

Gust of Toxins 1BB
Instant
When you cast ~, any player may pay 5 life. If a player does, counter ~.
All creatures get -5/-5 until end of turn.

Yawgmoth of Halcyon 3WW
Legendary Creature - Human Cleric
If damage would be dealt to a creature you control, prevent that damage and put a -1/-1 counter on that creature.
If damage would be dealt to you, prevent that damage and you lose 2 life.
Pay 2 life: Remove a -1/-1 counter from target creature.
2/4

Next: A legend that transforms into a legendary equipment or vehicle.

Festival of Flaying
Instant
Replicate (When you cast this spell, copy it for each time you paid its replicate cost. You may choose new targets for the copies.)
Target creature gets -1/-1 until end of turn.

The Power of Knowledge 2UU
Legendary Enchantment
Players skip their untap steps.
At the beginning of each player's upkeep, that player untaps X permanents he or she controls, where X is the number of cards in his or her hand.