I've seen a lot of the recurring games from the Wizards forums make the jump, but I don't see this one.
The idea is simple, for each converted mana cost from zero to ten, each poster takes turns designing a card of the appropriate color for that cost.

For the zero card you can design a spell without a manacost (such as Living End or Evermind) or a land of the given color identity (Kher Keep or Tolaria West).

When we get to cmc 10, you can either keep going or start over at the next color in the cycle.

We'll use the typical order
white
blue
black
red
green
traditional gold
hybrid
colorless

then start over.

I'll go first.

Pact of Solitude

Instant (R)
(white color indicator)
Destroy all creatures.
At the beginning of your upkeep, pay or lose the game.

Now the next player makes a 1 mana white spell, and the next makes a 2 mana white spell and so on.

Scout Hare -
Creature - Rabbit
Exalted
: ~ gains your choice of mountainwalk, forestwalk, or plainswalk until end of turn.
0/1

Tamer Of The Wilds
Creature - Human Cleric
Creatures you control are not monstrous.
1/3
"A song to Heliod's gloy, played on a lyre of olive wood will pacify any manner of savage beast" - Retoricles the Elder.

Seems like a neat build around card.

Cleanliness and Sorting
Enchantment
Each time you scry, you gain 2 life.
,: Scry 1.

Battlefield Protector
Creature - Human Cleric
: Target creature other than Battlefield Protector gains protection from the color of your choice until end of turn.
: All other creatures you control gain +0/+2 until end of turn.
1/2

Smite the Unworthy

Sorcery (M)
Destroy all non-Angel creatures.

Lordly Feud
Sorcery
Put two a 2/2 white knight creature tokens with vigilance onto the battlefield. Then, if ~ was cast the exile zone, copy it.
Rebound

So basically you get 12 power in tokens for 6 mana?

Oops. Its supposed to make one token.
Mixed two versions of the card.

Oops.

Ascend

Sorcery
Gain 10 life, then for each opponent you have more life than, draw two cards.

Sunrise Angel
Creature - Angel
Flying
When sunrise angel enters the battlefield and at the beginning of your upkeep, double your life total.
6/8

Angelic Mist
Enchantment Creature - Elemental Angel
Flying, Indestructible, Shroud, Defender
Enchantments opponents control lose all abilities while Angelic Mist in on the field. Opponents may not cast enchantments.
Creatures opponents control get -1/-0.
Other creatures you control get +0/+1.
2/10

Godsend

Sorcery (M)
Destroy all nonenchantment permanents.

Mystic Gain
(Blue Indicator) Instant
~ costs an additional unless you have drawn a card this turn.
Draw a card.

Grave Logic

Sorcery (C)
Look at the top card of your library. You may put it into your graveyard and repeat this process. Otherwise draw a card.

Not sure what the above is doing. I think maybe you mean into your graveyard?

Anyway...

Glacier King
Creature - Bird
Hexproof, Islandwalk
"The cleverest of penguins! They've adapted to slip through enchanted defenses upon frost mage fortresses in order to hide from seals."
2/1

Why do you put hexproof on all your cards?

Glacial Chill
Sorcery
Creatures you don't control don't untap during their controller's next untap step.
Draw a card.

I just happen to really like hexproof. Also it's a good way to represent resistance to magic, and minimize some elements of removal. And I don't put it on all my cards, heck not even half of them, just most of the appropriately colored ones (blue or green) and some of the others when it seems appropriate.

I don't only use hexproof, I also use shroud or protection from type effects as well when I deem they make more sense for balance and/or flavor.

Curb Instinct

Enchantment-Aura
Enchant red or green creature
You control enchanted creature.