Does it have a ability?
Anaba Ancestor

Does its mana cost include two or more ? (i.e. but not , for example.)
Dwarven Pony

Is it at Un-set or Portal (I mean from Portal to Portal 3 Kingdoms)?
Goblin Welder

Does it have a (printed) toughness of 1?
Sedge Troll

XX: It is not Green, White, or Blue.
XIX: It is not Extended legal.
XVIII: It is not Common.
XVII: It is a permanent.
XVI: It is not an Instant or Land.
XV: It does not have the word "Whenever" in its rules text.
XIV: It is a creature.
XIII: It is not colorless or multicolor.
XII: It is rare.
XI: It has a power of 3 or less.
X: It is red.
IX: It is has not been printed in the Masques block or later.
VIII: It has a converted mana cost of 3 or less.
VII: It does not have a ability.
VI: Its mana cost does not contain or more followed by .
V: It is not from an Unset or a Portal set.
IV: It does not have a printed toughness of 1.
Incorrect:
Daru Healer
Extirpate
About Face
Tolarian Academy
Ember Shot
Abyssal Nightstalker
Worldgorger Dragon
Endless Cockroach
Snake Basket
Zombie Master
Ball Lightning
Obstinate Familiar
Aladin
Anaba Ancestor
Dwarven Pony
Goblin Welder
Sedge Troll

Is it in a block?
Ydwen Efreet

Does it have X in it's cost?
Kobold Overlord

XX: It is not Green, White, or Blue.
XIX: It is not Extended legal.
XVIII: It is not Common.
XVII: It is a permanent.
XVI: It is not an Instant or Land.
XV: It does not have the word "Whenever" in its rules text.
XIV: It is a creature.
XIII: It is not colorless or multicolor.
XII: It is rare.
XI: It has a power of 3 or less.
X: It is red.
IX: It is has not been printed in the Masques block or later.
VIII: It has a converted mana cost of 3 or less.
VII: It does not have a ability.
VI: Its mana cost does not contain or more followed by .
V: It is not from an Unset or a Portal set.
IV: It does not have a printed toughness of 1.
III: It is not in a block.
II: It does have an in its mana cost.
The Romans don't have a 0, so I started at XX and now we're down to I...

Incorrect:
Daru Healer
Extirpate
About Face
Tolarian Academy
Ember Shot
Abyssal Nightstalker
Worldgorger Dragon
Endless Cockroach
Snake Basket
Zombie Master
Ball Lightning
Obstinate Familiar
Aladin
Anaba Ancestor
Dwarven Pony
Goblin Welder
Sedge Troll
Ydwen Efreet
Kobold Overlord

Rock Hydra - picked the wrong one of two!

Congratulation Picks, you got 1 point! (instead of me getting 15).
I knew the question meant you were getting close.
This also reassuring for me, 'cause I was afraid I made a mistake somewhere...

Well, it confused me 'cos I didn't find the efreet on the new gatherer, although it clearly fit. Anyway, I've got another card.

Opening the round (maybe) with popular question:

Is it multicolored or colorless?
Groundskeeper

u' Yes, it is multicolored or colorless.

Unlisted are:
Groundskeeper

Is it Extended-legal?
[card]Sisay's Ring[/card]

Is it Extended-legal?
[card]Sisay's Ring[/card]

u' Yes, it is multicolored or colorless.
T' Yes, it is Extended-legal.

Out of stock are:
Groundskeeper
Sisay's Ring

Is it Standard-legal?

Woolly Thoctar

u' Yes, it is multicolored or colorless.
T' Yes, it is Extended-legal.
s' Yes, it is standard-legal, and don't call me Woolly. :o

Not in taste are:
Groundskeeper
Sisay's Ring
Woolly Thoctar

Is it in the Shadowmoor block?
Nath of the Gilt-Leaf

Is it two colors?
Wistful Selkie

u' Yes, it is multicolored or colorless.
T' Yes, it is Extended-legal.
s' Yes, it is standard-legal, and don't call me Woolly. :o
p' Yes, it is in the Shadowmoor block.
n' No, it is not two colours.

Locked in the cellar are:
Groundskeeper
Sisay's Ring
Woolly Thoctar
Nath of the Gilt Leaf
Wistful Selkie

Is it common or uncommon?

Cauldron of Souls

Is it a creature?
Watchwing Scarecrow

Is it a Scarecrow?
Reaper King

u' Yes, it is multicolored or colorless.
T' Yes, it is Extended-legal.
s' Yes, it is standard-legal, and don't call me Woolly. :o
p' Yes, it is in the Shadowmoor block.
n' No, it is not two colours.
o' No, it is not common or uncommon.
x' No, it is not a creature.
v' No, it is not a Scarecrow.

Thrown in the compost bin are:
Groundskeeper
Sisay's Ring
Woolly Thoctar
Nath of the Gilt Leaf
Wistful Selkie
Cauldron of Souls
Watchwing Scarecrow
Reaper King

Was it illustrated by Rob Brown?

Leering Emblem

Is it an Equipment?
Leering Emblem

Does it have a white mana symbol in its text box?
Flooded Grove

Is it named Ward of Bones?

Ward of Bones

@ALEX: Your guess is the same as Idle Muse.

There was like three edits going there... Not sure what happened.

u' Yes, it is multicolored or colorless.
T' Yes, it is Extended-legal.
s' Yes, it is standard-legal, and don't call me Woolly. :o
p' Yes, it is in the Shadowmoor block.
n' No, it is not two colours.
o' No, it is not common or uncommon.
ξ' No, it is not a creature.
v' No, it is not a Scarecrow.
μ' No, it was not illustrated by Rob Brown.
λ' No, it is not an equipment.
κ' No, it does not have a white mana symbol in its text.
ι' No, it is not named Ward of Bones.

Rotten tomatos are:
Groundskeeper
Sisay's Ring
Woolly Thoctar
Nath of the Gilt Leaf
Wistful Selkie
Cauldron of Souls
Watchwing Scarecrow
Reaper King
Leering Emblem
The other leering emblem
Flooded Grove
Ward of Bones

Is it a land?

Reflecting Pool

u' Yes, it is multicolored or colorless.
T' Yes, it is Extended-legal.
s' Yes, it is standard-legal, and don't call me Woolly. :o
p' Yes, it is in the Shadowmoor block.
n' No, it is not two colours.
o' No, it is not common or uncommon.
ξ' No, it is not a creature.
v' No, it is not a Scarecrow.
μ' No, it was not illustrated by Rob Brown.
λ' No, it is not an equipment.
κ' No, it does not have a white mana symbol in its text.
ι' No, it is not named Ward of Bones.
θ' Yes, it is a land.

Fresh flies are:
Groundskeeper
Sisay's Ring
Woolly Thoctar
Nath of the Gilt Leaf
Wistful Selkie
Cauldron of Souls
Watchwing Scarecrow
Reaper King
Leering Emblem
The other leering emblem
Flooded Grove
Ward of Bones
Reflecting Pool

Does it have a in the text box?

Springjack Pasture.

Does it have a land type? (forest, plains, etc.)
Madblind Mountain

u' Yes, it is multicolored or colorless.
T' Yes, it is Extended-legal.
s' Yes, it is standard-legal, and don't call me Woolly. :o
p' Yes, it is in the Shadowmoor block.
n' No, it is not two colours.
o' No, it is not common or uncommon.
ξ' No, it is not a creature.
v' No, it is not a Scarecrow.
μ' No, it was not illustrated by Rob Brown.
λ' No, it is not an equipment.
κ' No, it does not have a white mana symbol in its text.
ι' No, it is not named Ward of Bones.
θ' Yes, it is a land.
n' Yes, it has a in the text box.
ζ' Yes, it is has a land type.

Spat out were:
Groundskeeper
Sisay's Ring
Woolly Thoctar
Nath of the Gilt Leaf
Wistful Selkie
Cauldron of Souls
Watchwing Scarecrow
Reaper King
Leering Emblem
The other leering emblem
Flooded Grove
Ward of Bones
Reflecting Pool
Springjack Pastures
Madblind Mountains

Is it on Eventide?

Island

Hehe, yes it's an Island
Ulxiz wins with ε' points.

Since this was a weird one, I just wanted to highlight a couple of interesting questions.

p' Yes, it is in the Shadowmoor block. <- Obviously whatever you suggested here would work...
o' No, it is not common or uncommon. <- Technically, basic lands have been commons previously, but not in Shadowmoor where they get their 'basic land' rarity, so I had to go with that.
μ' No, it was not illustrated by Rob Brown. <-- I was really hoping he had drawn an Island somewhere because that would have confused you like mad. Too bad
ι' No, it is not named Ward of Bones. <-- At this point I knew the confusion had hit, but I also knew that you would twig once I answered this lot.

n' Yes, it has a Blue mana symbol in the text box. <-- Ah... This was interesting. Does a watermark count as a blue mana symbol? Had you phrased it a different way (rules text) then I would have had to draw on the rules which say Basic Lands are assumed to contain the text , add [mana symbol] to your mana pool. In both cases, previous versions have had it on the card, but not in Shadowmoor. Both of these are slightly ambiguous, but I went with the spirit of the question.

Wow! Nice one, Picks.

Anyway, now onto the game: What card i'm thinking of?

Fafnir - 25
Picks-at-Flies - 22
Ulxiz - 14
ALEX Ryugami - 10
innuendo - 6
Idle Muse - 6
Aurora Illumina - 6
emperorkingx - 2

Is it white, blue, or black?
Coral Trickster

Has it been printed more than once?
Fat Ass <-- Wouldn't it be amazing if one of these random guesses at the beginning was right? Only 10365 cards to choose from!

Is it monocolored?
Thundermare

Answers
20. No, it's not white, blue or black.
19. No it hasn't been printed more than once.
18. Yes, it's monocolored.

Bad Guesses
Coral Trickster
Fat Ass
Thundermare

Is it extended-legal?
Thousand-legged Kami

Answers
20. No, it's not white, blue or black.
19. No it hasn't been printed more than once.
18. Yes, it's monocolored.
17. No, it's not extended-legal.

Bad Guesses
Coral Trickster
Fat Ass
Thundermare
Thousand-legged Kami

Is it Red?
Rock Hydra

Answers
20. No, it's not white, blue or black.
19. No it hasn't been printed more than once.
18. Yes, it's monocolored.
17. No, it's not extended-legal.
16. No, it isn't red.

Bad Guesses
Coral Trickster
Fat Ass
Thundermare
Thousand-legged Kami
Rock Hydra

Is it a permanent?
[card]Evincar's Justice[/card]

Has it been printed in any set that has (at some point) been standard legal, from Urza's Block onwards? (i.e. not from an early set, Un-set or portally type thing.)
Elvish Impersonators

Answers
20. No, it's not white, blue or black.
19. No it hasn't been printed more than once.
18. Yes, it's monocolored.
17. No, it's not extended-legal.
16. No, it isn't red.
15. Yes, it is a permanent.
14. No, it has not been printed on a set ,from Urza's block and onwards, that has been standard legal.

Bad Guesses
Coral Trickster
Fat Ass
Thundermare
Thousand-legged Kami
Rock Hydra
Evincar's Justice
Elvish Impersonators