To use an example from Planar Chaos, let's say I felt that white should have regeneration. I would then make two white creatures with regeneration. I could then go on to design Revered Dead and Dawn Charm. Note that Revered Dead happens to be a color-shifted Drudge Skeleton. I wasn't really looking for those, but I'm not about to tell you how to do your challenge. Maybe, however, you could include the straight-up color-shifted card as a bonus third card entry?

Oh, and also, I kind of assumed that designers wouldn't take mechanics that were already shifted recently, or shifted in Planar Chaos. The point, to me, is to find and explore new space. But again, that's your call.

Oh, cool idea!

For the record, Rosewater has a list of which mechanics where already shifted in Planar Chaos I:

http://www.wizards.com/Magic/Magazine/Article.aspx?x=mtgcom/daily/mr263
http://www.wizards.com/Magic/Magazine/Article.aspx?x=mtgcom/daily/mr265

Slowblink into red: Force Through, Goblin Jailer

Red gets Islandwalk. Blue is Red's enemy. Freshwater fishes and red Pirates. Goblin Vikings

Most of the major mechanics were shifted in Planar Chaos, so I would say it's fine to choose a mechanic that was shifted in PC 1; just shift it somewhere else :)

But for my submission, I moved deathtouch into white. Burning Seraph, Too Holy To Touch.

I'm not sure this is a good idea, but I decided to swap "direct damage for 1 and 2" and "primary in trample" between red and green.

Full explanation on Thornbite Shaman. Also Scorpion Sting in green. And Arc Elemental and Yavimaya Firewurm in red.

red already gets trample. the PC trample sliver is red. lorwyn red giants have trample. chaos imps in RTR etc.

i also dont get the obsession over green direct damage. it's only interesting if it's incidental, like hurricane. or perhaps reactive damage; natural defense mechanism; hexproof variant. Prickled Rose, Silverback Scorpion.

another idea i had is minor lifegain in blue in place of cantripping or scrying.

I had thought exalted fit black, but M13 beat me. I'll go with unearth in green.

­Eternal Druid ­Resilient Thallid

Green is a graveyard color and a creature color. It's not uncommon for them to have "dies" triggers. So it's a perfect candidate mechanically. Philosophically, green views everything as a system, so it's cool that these unearth creatures can, after dying, still leave something of value. This is why I'd not center them around a "last ditch effort" flavor, and instead give them relevant abilities that feel like they still contribute with their last breath.

If we're going the Planar Chaos way, though, where green got Groundbreaker, a green Hellspark Elemental would be cool.

"i also dont get the obsession over green direct damage."

I think it's forbidden fruit. People want to say "it sounds so wrong, but I can think of a way to do it well". I agree, having a specific sort of direct damage which makes sense in green is the best way to do it (and spiky hexproof is a good way to go for that).

I decided to take 'unsummon' and move it to white (on the justification that white already gets to exile stuff) Sun Demon
­Slight Banishing

For the pure colourshift; I'm tempted to go for straight up "Unsummon" - it was a very iconic card in its day; but is regarded as too weak usually, now. So maybe it's a viable candidate for shifting.

Oh wait; dammit; was this supposed to be an actual keyword? Drat.

I, uh, I went and coninued this in a different direction - shifting the titans into demons; and trying to colourshift them into different abilities a bit.

­Sun Demon Frost Demon Grave Demon Inferno Demon Primeval Demon

Not sure if that fits this challenge or not, really.

re: green direct damage

well there are 3 other colors who already cover pretty much everything to do with direct damage. so i don't see any value or excitement over a green shock. also red/green decks are so common and easy to build that the benefit isn't great either (green DD would cost more than red versions anyway). in short, green is like the last color when it comes to direct damage (even after colorless and blue). so i'm totally with Maro on this one: http://markrosewater.tumblr.com/post/24589663392/what-was-the-reasoning-for-printing-hornet-sting-was

other color shifts are cool because they're
1. only found in one color (discard, counterspell, wrath)
2. totally unexpected (red bounce, green vigilance)
3. rarely used (landwalk, one-set mechanics)

"was this supposed to be an actual keyword? " - No, not at all. Bounce is fine - it was already colourshifted in Planar Chaos, but your take on it is a little different. (White got to bounce its own creatures, Stonecloaker, while red got to bounce opponents' creatures, Stingscourger.)

On Unsummon: I still think it's a solid card. It mostly depends on the environment that its in. I remember when Blue-Green Madness came out. Aether Burst was originally part of the deck, because it's damn powerful. As the deck slowly perfected itself, though, the Aether Bursts were replaced by Unsummons. U/G needed a disruptive one-drop, and Unsummon fit the description. And it still does that for any deck who needs exactly that.

Or, to put it another way, the Gatherer rating for M13 Unsummon is at 4.19. Sounds in fashion to me.

Indeed. People were up in arms about what they perceived as a strictly better Unsummon, Vapor Snag, which was everywhere in tournaments. (It's not quite strictly better because using it to save your own creatures costs you a life.) Unsummon is pretty classic... in fact, so much so that I'd say shifting it to another colour would be too strong, too much the kind of thing they avoided doing in Planar Chaos. They didn't print blue Coercion or blue Distress; they printed Piracy Charm, Riptide Pilferer, Venarian Glimmer and Dismal Failure. None of those are particularly strong, not strong enough to be playable in casual as an alternative to black discard.

Fair enough.

Not to drag this out, but Vapor Snag has a lower Gatherer rating than Unsummon: 3.98. Probably because, according to the control blue mage, losing one life one-third of the time isn't worth an opponent losing 1 life two-thirds of the time.

Added Plumebreaker and Unforgiving Skies.

­The Magnificent Steiner

Black kills, but sometimes an enemy just might be overwhelming. The Hellbent comes from an insatiable bloodlust. I couldn't come up with a good Magicy name so I took a reference to Monster that I thought was appropriate.