My Gatecrash spoiler this time around fits perfectly into my guild identity (though I may not be supposed to admit to this particular guild affiliation). I've always been a big fan of the Dimir, and am happy to get to talk about their Charm today:
As with all the Charms, Dimir Charm has three modes to choose from, and two of them are quite useful. The third isn't bad, but isn't quite as powerful as the other two, at least not until the lategame.
Let's look at what this does. First of all, it acts as removal. Killing a 2-power guy for two mana is decent, letting you handle most everything your opponent would play in the first few turns. As 1/3 of card, this is quite good.
Secondly, it's an [card]Envelop[/card] for two mana. Again, this isn't earth-shattering, but it's certainly not bad. This is likely the ability that will fluctuate in value the most of the three. There are always going to be some number of small creatures to kill, but whether or not you really want to stop sorceries specifically will definitely vary as the metagame shifts. Envelop was very relevant in Standard back during Odyssey's days, and a two-mana Envelop that kills creatures and has a third ability is definitely something to be aware of. Countering a sorcery is also likely to be the mode that gets you the biggest mana advantage, so I'm definitely looking to Dimir Charm when there are a lot of good sorceries running around.
The last ability is the only one that doesn't quite net you a full card every time. If you are killing a creature or countering a spell, clearly it's a one for one, but milling two of the top three of either player's deck is a net loss of a card. That doesn't mean this is bad, and there are spots where it's easily worth a card. The three most common scenarios where this is good are the following:
1) It's late in the game, and drawing a land is completely irrelevant. Here, you can basically make your opponent skip a turn by putting a land (or a bad spell) on top of their deck. It's unlikely that you won't find one in the top three cards, and if they aren't doing much, this is very good.
2) You are digging for one specific card, and are willing to sacrifice cards to get there. If you hit the Supreme Verdict or Sphinx's Revelation you need, who cares that the Dimir Charm is technically minus one card? Some control decks will play this as a removal/counter, and just use it to dig for Revelation once the game has progressed enough.
3) You are using the graveyard as a resource. Milling a Lingering Souls or a Think Twice mitigates the loss of a card significantly, and again points towards an Esper-colored control deck of some kind.
Overall this is a solid card for Constructed. It won't be right for every metagame, but this kind of flexibility usually sees some play. A counter/removal with some interesting [card]Time Walk[/card]/[card]Impulse[/card] potential is not something you should ignore.
For Limited, this is very good. Even if it was just the creature kill, it would be good, and adding the extra modes is just gravy. Countering a sorcery won't come up incredibly often, but when it does, it should be great. Sorceries are usually expensive and game-altering, so suddenly knocking the opponent's legs out from under them should be very good. The last ability is slightly worse than in Constructed, at least from a digging perspective, just because you are less likely to have insanely powerful cards in your deck. On the other hand, mill is a Dimir theme, so milling them for two could be sweet value.
Overall I like this card, and feel that it appropriately represents my guild's interests.