MTG Salvation

Trailblazer Scout is nutty if you cast it for GG and almost certainly needs to be smaller. 2/1 might be acceptable.

Spiteful Wishgranting :1mana::symb:
Sorcery
Search your library for a card and put it in your hand, then shuffle your library. Then an opponent chooses one - destroy target creature of that opponent's choice, or you discard two cards, or you lose 5 life.

Pumpkin King 3BB
Legendary Creature - Plant Skeleton
Haste, intimidate
:symtap:: Return target creature card from a graveyard to the battlefield under your control and exile Pumpkin King. That creature gains haste. At the beginning of the next end step, exile that creature and return Pumpkin King to the battlefield tapped.
4/2

Orgone Conduit 3
Artifact
Tap two untapped creatures you control: Add one mana of any color to your mana pool.

Wilderness Sympathy 1G
Enchantment - Aura
Enchant creature
Enchanted creature is a Werewolf in addition to its other types and has ":symtap:: Add GG to your mana pool."
At the beginning of each upkeep, if no spells were cast last turn, transform Wilderness Sympathy.
//
Wilderness Expression
(G) Enchantment - Aura
Enchant creature
Enchanted creature gets +3/+3, is a Werewolf, and has "GG: Regenerate this creature."
At the begenning of each upkeep, if a player cast two or more spells last turn, transform Wilderness Expression.

Bandersnatch Hunting 2RU
Creature - Beast
Haste, first strike
When Bandersnatch Hunting becomes blocked by two or more creatures, return it to its owner's hand.
3/1

EDIT: One I forgot:

Hastur Hastur Hastur CC
Enchantment
When an opponent casts a creature spell, pay and sacrifice Hastur Hastur Hastur. If you do, search your library for a creature card with converted mana cost X or less and put it onto the battlefield.

I'm not sure what color this should be, although I think it could fit in any of white, green, or black.

I made one of these, myself.

Mercurial Spring
Land
Mercurial Springs enters the battlefield tapped.
:symtap:: Add or to your mana pool.
UR: Until end of turn, Mercurial Springs becomes a 1/5 red and blue Elemental creature with "2: Switch Mercurial Spring's power and toughness until end of turn." It's still a land.

EDIT: Oh right. Jeez, I can't believe I did that.

You can't activate abilities while you're casting spells. You can either drop the activation restriction from the abilities, or you can change their activated abilities to "As an additional cost to cast an instant or sorcery spell, you may pay *manacost* and tap ~. If you do, that spell gains *effect*."

Sword of Faith and Family 3
Artifact - Equipment
Equipped creature gets +2/+2 and has protection from green and from white.
When equipped creature deals damage to a player, untap all creatures you control, then search your library for a card with the same name as equipped creature, reveal it, and put it in your hand, then shuffle your library.
Equip 2

Sword of Secrets and Lies 3
Artifact - Equipment
Equipped creature has protection from blue and from black.
Whenever equipped creature deals damage to a player, return target creature that player controls to its owner's hand, then search that player's library for two cards and exile them.
Equip 2

Quote from Clairval

Malevolant Graymalkin - I don't get the flavor (perhaps not enough english vocabulary).

A "greymalkin" is an old or evil-looking female cat. Pretty much just for that it has associations with witchcraft and evil. The flavor is that it curses the creatures that kill it.

Guardians of Ulthar - Sideboard card for one specific archetype (Cats aggro) against one specific archetype (BX aggro) => very narrow card. Not to say such a slow threat will automatically eat black removal, making it inefficient on the turn it enters the battlefield, unless you have 3WWWW. Which is a lot. Junk rare awating for an awesome casual combo.

I envisioned it more as an uncommon for Limited, with a few cats scattered around the rest of the set/block like the Splicers in Scars block.

"Sword of Truth and Beauty" or "Sword of Theory and Practice", perhaps?

EDIT: Another one I thought of:

Sword of Death and Destruction 3
Artifact - Equipment
Equipped creature gets +2/+2 and has protection from Red and Black.
When equipped creature deals damage to a player, destroy target artifact that player controls and he or she loses 3 life.
Equip 2

Household Hunter 1G
Creature - Cat
When Household Hunter enters the battlefield, you may have it fight target Bird, Insect, Rat, or Spider creature.
2/2

Malevolent Greymalkin 2B
Creature - Cat
When Malevolent Greymalkin dies, destroy each creature that dealt damage to it this turn, then each player discards a card for each creature he or she controls that was destroyed this way.
2/2

Guardians of Ulthar 3WW
Creature - Cat
Whenever Guardians of Ulthar or another Cat creature dies, you may pay WW. If you do, exile up to one target black creature and put a +1/+1 counter on each Cat creature you control.
3/3

You have to drop the "instead" and use the Clergy of the Holy Nimbus wording. Otherwise, gaining a regeneration shield replaces the destruction event in its entirety.

I still think the activated ability is better because it lets you have a creature die if that's what you want.

The replacement effect protects it from destruction twice, though. "If it would be destroyed, instead remove a +1/+1 counter from it and regenerate it." That a) prevents the current instance of destruction and b) gives a regeneration shield. If it was destroyed from lethal damage, it then gets destroyed again and uses up its regeneration shield, but if it was (say) Doom Bladed, it just ends up having a regeneration shield. The activated ability works better.

Quote from Froxbite

Since when is vigilance green?

Since a few years ago. It's still pretty rare, but it pops up now and then.

Goblin Groinpuncher 3R
Creature - Goblin Rogue
When Goblin Groinpuncher attacks, it deals 1 damage to target creature. Tap that creature.
"The first trick is, don't let 'em see you coming. The second trick is, don't stick around too long."
2/2

Repercussions of Evil 2B
Enchantment - Aura
Enchant creature
Enchanted creature gets +3/+3 and has "When this creature dies, return it to the battlefield under target opponent's control. It becomes a black Zombie in addition to its other types and colors."
Those who wish to defeat their enemies at any cost often find that it costs more than they expected.


EDITED:
Dreampath Guide 1WU
Creature - Human Scout
When Dreampath Guide attacks, exile target attacking creature. After blockers are declared, return it to the battlefield under your control tapped and attacking.
1/2


It's worth noting, I think, that if Dreampath Guide doesn't target itself it can just get blocked, Geist of Saint Traft style.

Tusked Behemoth pulls the same trick - in GW it's W giving First Strike and G giving Vigilance; in RW it's R giving first strike and W giving vigilance.

Tidehollow Gargoyle almost does it too, but since both Black and White get both flying and lifelinkit doesn't quite.

A couple of more cards, to maybe entice someone into responding.

Recant 1U
Instant
Return target spell or permanent you own to your hand.
Draw a card.

Pearlnode Field
Land
:symtap::Add 1 to your mana pool.
:2mana:, :symtap:: Put a mine counter on Pearlnode Field.
Add WW to your mana pool. Activate this ability only if Pearlnode Field has a mine counter on it.