Number Games?

[Charlie]

It may be interesting to make cards that deals with specific numbers of resources.

Random Removal
B
Instant
Choose a color. Reveal your hand. Destroy target creature if its power is equal to the number of cards of the chosen color in your hand.

Balanced 0-drop?
0
Artifact Creature - Gnome
-1/0
~ gets +1/+1 as long as there is exactly one basic plains in play.
~ gets +1/+1 as long as there is exactly one basic island in play.
~ gets +1/+1 as long as there is exactly one basic swamp in play.
~ gets +1/+1 as long as there is exactly one basic mountain in play.
~ gets +1/+1 as long as there is exactly one basic forest in play.

Card advantage engine
WU
Enchantment
At the beginning of your upkeep, you may reveal your hand. If the number of white cards in your hand is the same as the number of blue cards, draw a card.

[Anusien]

Make separate threads for each of these?  There's only the most tenuous of connections holding them together.

Random Removal: Not actually random, but wouldn't it make more sense to trigger off its toughness?

0-Drop: Yeah, I have to admit I'm not a fan of this.  I think it's trying too hard to be cute, and is often not going to be useful.  Also, a creature that is potentially a 4/5 should not cost 0.

Card Advantage Engine: This has the potential to be one of the best card advantage engines ever, for a small investment.  It's the kind of card that is either worthless or blowing your opponent out, and so I don't like it.

[Matt]

The engine one is broken with 0 white 0 blue.

[Charlie]

The engine one is broken with 0 white 0 blue.

yes, but only if you managed to play this with very light white and blue.
As for the mana cost, I'm not sure; I used Phyrexian Arena as reference, made it multicolor, and remove the life loss and put in another restriction, so it seemed WU or 1WU is fine?

[Norm4eva]

I think a more apt comparison would be Howling Mine.  It costs 2 and is symmetrical, but has no drawback.
It seems like it'd be pretty easy, even in a heavy UW deck, to overcome the drawback.  A critical mass of UW cards and Brainstorm would make sculpting your hand pretty simple.

[Venven]

I think this is interesting "design space". It would have been cool with the flip creatures from Kamigawa block. I think there are more intersting places for this "mechanic" than your examples, but that requires some serious time to ruminate.

For a single card there should be some way of affecting it's critical value (i.e. on card #2 "Sacrifice a land: search your library for a basic land card and put that card into play tapped. Then shuffle your library. Play this ability only once each turn."). For a block with the mechanic the cards could be pretty individual and the crossovers could reinforce colour relationships in the block.

How about a creature with a variable power and "When this creatures power is equal to 3 (or whatever) it becomes special."?

Your gnome could be a 2/2 for 3 (morph creature) that gets, say, first strike with a plains in play, trample with a forest in play, fear for swamp, etc. That's so boring, but the power level would be less frightening than with a possible 6/5 for 0. This whole vein of basic lands in play reminds me too much of the Invasion/Planeshift/Apocalypse, which is a mechanic I'd rather forget.

[parallax]

Your gnome could be a 2/2 for 3 (morph creature) that gets, say, first strike with a plains in play, trample with a forest in play, fear for swamp, etc. That's so boring, but the power level would be less frightening than with a possible 6/5 for 0. This whole vein of basic lands in play reminds me too much of the Invasion/Planeshift/Apocalypse, which is a mechanic I'd rather forget.

Tek

[Venven]

That's the guy. Couldn't think of the name or find him in my quick search. Anyways, forget that.

Edit: Although it is slightly different because it would be "exactly one plains" etc. and so could be cheaper. But I don't think Tek is a creature anyone is scrambling to bring back.

[Matt]

Actually, there's at least 570 people who are clamoring for Tek.

[Venven]

Actually, there's at least 570 people who are clamoring for Tek.

That could only have been an elaborate joke. No one really likes Tek.

[Venven]

Spent some time thinking about the "exactly" mechanic (I'm not even sure that word is necessary) and came up with some neat stuff... I think.

Land
T: Add 1 to your mana pool.
T: Add 1 mana of any color to your mana pool. Play this ability only if you control exactly 1 land.

Puppy Dog
Creature -- Dog
2/2
Pack 3: All Dogs get +1/+0.
Pack 4: Sacrifice ~this~.

I'm sure there's a good mix between flavour and functionality somewhere around here.

Sorcery
WUBRG
If you control exactly 5 lands, have exactly 5 cards in your hand and exactly 5 cards in your graveyard, you win the game.

The wording on this is terrible but I'm tired.

2
If each player has exactly 6 cards in his or her hand, ~this~ costs 1 less to play.
~This~ CIPT.
T: Add 1 to your mana pool.

Almost half a Sol Ring...

Oram
3GG
Creature -- Latnemele
*/*
Oram's power and toughness are each equal to 7 minus the number of cards in your hand.
When Oram's power is exactly 7, sacrifice Oram.

2BB
The Greatest
Creature -- Ninja Pie-writ Zombie Mutant Wizard
1/1
Ninjutsu 1UU
Whenever The Greatest deals damage to a player, that player sacrifices a permanent unless he or she pays 1.
T, Remove a creature card in your graveyard from the game: The Greatest deals 1 damage to target player, then return The Greatest to it's owner's hand.

This card is completely unrelated to the topic.

UU
Instant
If you are exactly 6 feet tall, you are 2 inches too tall.

And now I'm just being silly.

Engineering Conundrum
1UU
Sorcery
Reveal your hand. If the combined converted mana cost of all the cards in your hand is exactly 9, draw 3 cards. Otherwise, draw a card.

I could see a cycle of these. Makes me wish transmute wasn't so specific.

[chrissss]

I don't see how that 0 drop is too good.

There will almost never be exactly one land in play, because your opponent plays lands as well. so first turn a 0/1, then opponent plays a land, 1/2, then you play another land ( a different land than the lands in play) 2/3 then opponent plays a land, 1/2 again, etc.
If it said: " If you control exactly one land..." now this is different.

I like the random removal.

The card advantage engine is powerfull, especially with multicolor cards, and blues advantage of cards like brainstorm to get even more cards from the card drawer. I would up the mana to make it more balanced.