I tend to look at cards that bring something different or interesting to multiplayer formats. I like a good legendary creature, but my heart really gets pumping when I see the words "each opponent" on a card.
I thought I would take this chance to talk about some of the cards from Theros that I found particularly interesting. I'm not saying that these are the best multiplayer cards in Theros. Medomai the Ageless is a fun card for multiplayer games but it isn't made that much better by the format. I'm looking for cards that are just so much better because you added more opponents. A great example of this is...
Gray Merchant of Asphodel. This is at least a Syphon Soul with a 2/4 body attached. Odds are you'll have at least two other black permanents in play by the time this enters the battlefield, so you are probably taking 4 or 5 life from each opponent. In a four-player game, you can expect to gain 12 to 15 life when you play the Merchant—12 to 15 life for five mana is a ridiculous deal! Add in a way to flicker 1 the Merchant and things get ugly for everyone else. This isn't even suggesting you are mono-black. If you are really trying to up your devotion, I don't think getting devotion to eight is too crazy, particularly in black, where a double-black mana requirement for permanents is relatively common.
Agent of the Fates. Speaking of keeping your devotion count up, Agent of the Fates is a card that fits nicely in many black decks. Once you find a way to repeatedly target the Agent, you'll be able to handle most opponents' creatures, assuming they aren't running token decks. Any card that offers to take out several creatures for one spell (and none of those creatures are yours) needs to be considered. The Agent is a player.
Scholar of Athreos. Extort has proven to be a successful multiplayer ability. The Scholar essentially reads : Extort 1. I can't decide if having that ability is better than simply having an extort creature that does the same thing for one mana but needs a spell. I suspect later in the game, when you have nine mana available, using this ability three times at the end of your opponent's turn will either win you games or draw plenty of attention. Let me know if this card becomes a winner for you.
Steam Augury. Remember when you were little and your mom poured out two glasses of juice for you and your sibling. The two of you argued endlessly over who would get which glass because you both believed one of them had a drop more juice? That's Fact or Fiction. Later, your mom got smart and told you to pour the juice and your sibling got to pick which glass. That's Steam Augury.
I have heard so many people explain how this is a weaker Fact or Fiction and I get it. If your opponent is splitting the pile, he or she may not know what you need and could screw it up. Now, since you are setting up the piles, you are left with trying to either set up two even piles or fool your opponent into giving you the card(s) you want.
The joy of Steam Augury is basically the same as Fact or Fiction in multiplayer. You get to pick which opponent is going to choose. If you are leading, or will likely be dominating the board if you get a particular card out of the five you are looking at, then you are looking for the sucker at the table who is going to pick the correct stack. If you are fighting with an opponent who is the Clear Threat at the table, you are going to split the piles into two stacks, five in one stack and zero in the other, and have a player who is currently an ally give you the five cards so you can use them against the Clear Threat.
Ember Swallower. I think of this guy as the setup. You will play it regularly and use the monstrous. If anyone in your group is holding extra lands to bluff cards in hand, they will start dumping those extra lands on the board to avoid getting shafted when everyone is forced to sacrifice three lands. Once you have everyone dumping their lands, switch to the land destruction deck you have been dying to play and destroy them all! Muhahaha!
Actually, the question you need to ask yourself at that point is whether it isn't just the Ember Swallower that is monstrous. Yes, he wipes out a bunch of lands and that crushes players, but you have just led your playgroup to a monstrous place. Land destruction decks moving through your play group limits all the great and amazing plays that could be happening. You may win more games in the short term, but all anyone will remember is the time they could have done something awesome, but you played Ember Swallower and wrecked it.
Erebos, God of the Dead. This is where you are going to spend all that life you gained with the Gray Merchant of Asphodel. Getting your devotion to five shouldn't be too difficult. The Merchant and Erebos alone get you to three. I'm sure you can work out two more black mana symbols.
Even if you can't, Erebos as an enchantment is a powerful thing in multiplayer. Preventing your opponents from gaining life keeps many games from spiraling into that endless game that seems to drag on forever. Drawing cards for a couple of mana and a couple of life tends to be a small price to pay. If you happen to add a 5/7 indestructible body to the mix, all the better.
Hythonia the Cruel. The ability to kill off all of your opponents' creatures is always going to be a great effect for a multiplayer game. My concern with Hythonia is the prohibitive cost. Paying six mana, then eight mana, can be a real trick. Add to that a creature that has no protection from removal, and I'm not sure it is worth it. If a 4/6 deathtouch creature for six works for you, I'd tell you to run this and enjoy the possible upside. If not, then walk away. Relying on Hythonia's eight mana monstrous effect to make the creature any good is probably a mistake.
Nighthowler. When your power and toughness is based on the number of creatures in graveyards, you are going to be a better multiplayer card. The idea that you can bestow a bonus that will often amount to more than +5/+5 for four mana makes this a great card.
Purphoros, God of the Forge. "...2 damage to each opponent." I really shouldn't need to go any further. Making Purphoros into a creature is practically irrelevant. This card exists as a way to add extra damage. You can drop this card early enough in a game that Mogg War Marshall then lets you do 6 damage to each player for three mana. Purphoros is going to end games in a hurry. Mogg War Marshall is just one way; red has plenty of ways to produce many creatures very quickly. I, however, prefer to go for the big play:
With Purphoros in play, Army of the Damned does 26 damage to each opponent. It will be up to you to make sure all of your opponents stay at or below 26 life until then. I intentionally stayed primarily red in a half-hearted effort to get to five devotion. If I can build the deck to get a 6/5 indestructible creature without the deck suffering, why not?
Reaper of the Wilds. Creatures die in multiplayer. Often. The ability to scry each time one of them dies means you will draw lands when you need them and action when you need it. Thankfully, creatures with this kind of utility are normally quite small and fragile.
Oh, Reaper of the Wilds is a 4/5 creature you say? Well, thankfully you can just use a removal spell to...
Oh, hexproof on command? Well I'm not thrilled about using a fatty to block it but this thing has to go.
What do you mean it has deathtouch! Oh come on!
This is one of those cards that will provide you with steady, incremental advantage through the game, and force your opponents to use some of their best resources to get rid of it.
Stormbreath Dragon. There are an awful lot of creatures that can do damage outside the combat step. There are far fewer that do damage to every opponent. That would appear to make this guy an all-star, but take care when you play Stormbreath in your group games. Stormbreath Dragon is particularly harsh toward the control players in your group. Those players who load their hands with answers for various cards are the ones who will suffer the most when monstrous is activated. Think about that for a minute.
The players most able to deal with Stormbreath Dragon are the ones who will be hurt the most by it. To use this card successfully, you'll need to try and cast it when the likelihood of it getting countered is low. This means you'll want to cast it when players have fewer cards in hand, then you want to wait until players have cards in hand to maximize the monstrous effect. Between counters, bounce spells, direct damage, and creature destruction, you are asking for an awful lot when trying to use Stormbreath Dragon to its maximum potential.
Prophet of Kruphix. This list is not in a particular order, but I saved Prophet of Kruphix for last, because it is the best card in the set. Seedborn Muse has been a veteran stalwart in multiplayer games for years. The ability to untap on each upkeep means that you always have mana available for any spell you need to play. Decks with Seedborn Muse and cards that give you a place to sink all that mana (Omnath is probably the most popular one right now) are common in most play groups. A card that does the same thing as Seedborn Muse, albeit in two colors, is bound to be popular.
Then it gives all your creatures flash.
One of the big restraints on the old Seedborn Muse decks was that you couldn't play your creatures on your opponent's turns. Sure, many decks would also run Teferi, Alchemist's Refuge or Winding Canyon to get around that, but it would mean that you needed to have two different cards just to be able to cast your expensive fatties on other players' turns. Prophet of Kruphix wraps it all up in one neat creature. Being able to untap all your lands and creatures each turn while all your creatures have flash provides you with so many more options. Everyone has to wonder if you have a surprise blocker every time they consider attacking you. With flash, all of your creatures essentially have haste, since you can play them on your opponent's end step. This also means that if you have three huge creatures in hand, you could play one out on each opponent's turn, putting you way ahead of everyone else at the table. Expect Prophet of Kruphix to be a monster in your upcoming games.
1: Flicker is Magic slang for removing a creature from the battlefield, then immediately returning the creature to the battlefield. This lets you get the creature's "enter the battlefield" abilities again, or remove any tokens that have accumulated on an opponent's creature. (return)