Lucky Djinn
How much would you pay for a 5/5 flying creature?
That's kind of a tough question to answer, at least in straight mana costs; this is in part because there aren't a whole lot of (otherwise vanilla) 5/5 flying creatures you would want to play.
Which exemplars do you plan to peg your answer against? Take this one, for instance:
Pretty good 5/5 flier.
Is "six" the "right" answer then?
I don't think it can be; or at least I don't think "six" can be a simple and satisfying answer. Because Keiga, the Tide Star isn't just a 5/5 flier. Among other things, Keiga triggers a hell of a going away present if and when it dies. That's what made Keiga, the Tide Star one of the best-ever creatures to tap out for in the midgame.
In most cases? You get a nice big 5/5 flying creature. Really not an attractive blocker to attack into for the opponent; Keiga was bigger than most creatures the opponent could throw into it.
And if that opponent could somehow kill it?
You were going to take your opponent's best thing!
It didn't matter if that best thing was a 2/2 Skyknight Legionnaire or an absurd, time traveling, 15/15 Emrakul, the Aeons Torn. If you were going to tap out for Keiga, the Tide Star, there was an implied insurance policy involved.
So Keiga, the Tide Star was not only a 5/5 flying creature, but a 5/5 flying creature with an exceptionally powerful additional ability; contextually awesome in formats where creature combat mattered.
So, in theory, on Keiga we were paying six not just for a 5/5 flier, but for all that extra text. Are we paying more for Keiga, then?
"Legendary" = Discount
It is in fact the case that Keiga, the Tide Star came to players at a discount. 
would generally fall into the more expensive casting costs category, but Keiga was arguably aggressively undercosted! Who knows what it would have cost as a nonlegendary creature? (Being legendary is meant to be a disadvantage.)
Of course, being legendary actually gave the historical Keiga an interesting angle to exploit. Under the previous incarnation of the legend rule, you could play two copies of Keiga, the Tide Star, bury them both, and steal your opponent's two best creatures.
Today, a second copy of Keiga, the Tide Star need not rot in your hand. You get to keep one, and will still get the "Control Magic" upside on the other.
So I ask you again...
How much would you pay for a 5/5 flying creature?
Would you pay six mana total for a conjectural, straight-up 5/5 flier? Keiga was six with an advantage and a disadvantage both. This leads me to believe you would not pay six. In fact, for six, most players would be expecting some fairly game-breaking 5/5 fliers...
For that matter, "six" can mean different things at different levels of color-intensiveness. Compare...
 |
Ryusei's colored mana falls while Jugan's rises.
Multicolored six-mana creatures will, for that matter, fluctuate in size. The notion of being 5/5 itself ceases to be constant. Consider...
Point being, "six" is not a satisfying answer.
What about five mana? Is five mana a good deal for a 5/5 flier?
No.
For five mana, the expectation is probably a good deal more than a "mere" 5/5 flier.
It's going to be tough to find the casting cost we will be happy with for an otherwise vanilla 5/5.
Often, we will have creatures like Thundermaw Hellkite—admittedly a little too awesome at five—or legendary creatures that are also a bit more than vanilla at six (or in the cases of many sixes, not even 5/5).
What does all this mean, practically?
The answer is that I don't know how much we should pay straight up for a 5/5 flier.
I am skeptical you would get a lot of buyers at five mana. Thundermaw Hellkite was well-regarded, but Stormbreath Dragon—a sometimes 4/4 and sometimes bigger—with a base cost of five and a list of abilities my arm long is only sporadically played in Standard decks based on haste (one of Stormbreath Dragon's many abilities). I think most of us can generally agree that Stormbreath Dragon is better than any old 5/5, even if it's only a 4/4.
You clearly want more than "just" a 5/5 for six.
So how about four mana?
Well, at four mana we have a playable range that looks something like this:
And by "playable range" we mean there is no guarantee that Rathi Dragon would ever see play today, Flame-Wreathed Phoenix has proven itself essentially zero times in competitive tournament finishes, and Fledgling Dragon—dear, beloved Fledgling Dragon—was not even a 5/5 all the time.
So on four mana we still don't have our 5/5.
What we do have is this:
A 6/6 is much bigger than a 5/5; and Desecration Demon is sometimes much, much bigger than a 6/6! Unfortunately, it is often hanging out at the beach with sunglasses on and a daiquiri while the hordes are storming the castle walls and planking the local peasantry.
As with some of the legendary Dragons, this is a creature that offers more than just size, but also some downsides that need to be considered.
I think ultimately—and this is going to seem like a mite of a copout—there isn't any answer to what we would pay for a straight 5/5 flier, because we're never going to get a straight 5/5 flier.
What we are going to get is a 5/5 flier for a "discount" (which is weird because we aren't pegging it to any particular casting cost in 2014), but we will have to accept some potentially harsh tradeoffs.
Here are some non-5/5 comparables:
Cross-generation all-star. Interestingly, served first when Pyroblast was popular; most recently—and this was about a decade ago—that 6th toughness made it a fine foil to Blastoderm.
Not particularly less storied of a career than the harder-to-kill and more ability-laden Sengir Vampire.
In 2014, it is much more likely for us to get a good creature—with a powerful body or a great combination of abilities—for less mana than might seem altogether fair... but with some trade-offs or penalties. Here are some examples:
The Small or Cosmetic Penalty
Many Erhnam Djinn decks didn't even play Forests.
Legendary
Legendary is often used to tweak the cost of a creature ever so slightly without adding additional downsides.
A Little Bit of Life
Juzám Djinn was considered well and truly undercosted circa Arabian Nights (compare today to Polukranos, World Eater)... but Herald of Torment is still considered a good deal in 2014.
Intense Colors
All of these creatures are aggressively costed in one way or another. From a total/objective amount of mana, none of them seem too far out of line, but they do ask for concessions. For example, Demigod of Revenge decks in Standard typically had to skip Mutavault and RWU decks with Boros Reckoner generally played 0 basic Islands.
Giving Up Mana
These kinds of cards can have no drawback (if the opponent has no creature) or a substantial drawback (if the opponent has an expensive/legendary creature).
Giving Up Cards
Of the various kinds of downsides and limitations that help lower the mana counts of aggressively costed creatures, some matter relatively little, but might limit the cross-archetype popularity of certain cards (Boros Reckoner); others—specifically life loss—can be very unpopular among new players.
But the most eyebrow-raising by far tend to be cards that give up card advantage directly.
Despite potential card advantage given up from the very first turn, Goblin Guide has been a spectacularly successful offensive creature all the way up to Legacy.
Which brings us to this week's Journey into Nyx preview... Master of the Feast!
For me, Master of the Feast is a tough card to evaluate.
Of course, it is also quite obviously the reason we asked about costing a 5/5 flier at the beginning of this article.
In the abstract, a 5/5 flying creature for only three mana would be considered quite the steal. Currently, Herald of Torment—only 3/3—is a centerpiece threat in Standard... and it has a not-insignificant downside.
The closest card I can peg Master of the Feast to is Indentured Djinn (or "Lucky Djinn").
Lucky Djinn.
Indentured Djinn was a card that some very good players tried to play, but was never consistently good enough for Standard.
A 4/4 flier early on could win the game in five swings.
The problem was that Indentured Djinn would often give the opponent exactly what he or she needed to deal with the Djinn. You would need a little luck (note the name lucky) to hold a lead before the opponent drew the cards necessary to answer it.
Master of the Feast has two important distinctions relative to the Djinn.
First, 5/5 is bigger than 4/4.
As a 5/5 creature, Master of the Feast can end the game one swing faster than Indentured Djinn, in isolation.
Second, Master of the Feast gives the opponent a card per turn instead of a one-turn burst of cards.
If you already have a lead from other attacking creatures, playing Master of the Feast may give the opponent no immediate card advantage; and if you can win relatively quickly, your opponent may only draw one extra card or so.
But on the other hand, if he or she has a Pacifism or some odd, Master of the Feast is going to make for a very, very bad spot. A locked-down Master of the Feast actually makes for a one-sided Howling Mine for the other player.
Master of the Feast vs. Goblin Guide
Although Indentured Djinn seems like the more direct comparison—and one likely won by Master of the Feast on size and speed of card economy—the combination of fundamental costing and progressive, incremental, card economy does actually beg some comparisons to Goblin Guide. If Goblin Guide could be so good... is that a possible signal for Master of the Feast?
Master of the Feast | Art by Chris Rahn
Size and Abilities
What is better, a 2/2 hasty for one or a 5/5 flier for three? I think they both fall into the "this is better than you should probably get" category and leave it at that.
Certainty of Card Advantage
The bigger gulf is that Goblin Guide might never give the opponent an extra card. Goblin Guide might be in the red zone on turn one and hit for all 20 while the opponent keeps revealing some nonland or other. Master of the Feast is always going to give up that card, turn after turn, for as long as we have him.
Further, Goblin Guide only gives up extra lands. In some formats—for example, Legacy is one of the main formats Goblin Guide sees play—Brainstorm opponents can turn those lands into legit extra cards... but that at least requires work. On a fundamental basis, Goblin Guide is less likely to fuel an answer for itself (or the opponent's forward plan) than is Master of the Feast.
If you are in a position where Goblin Guide card economy would sink you... you can just not attack. Master of the Feast is never going to give you that option.
But ultimately, at some point, a 2/2 will no longer benefit from haste (that is a first-turn thing only) and Master of the Feast only needs to stick around unchecked for four turns to win.
How excited can we be?
Master of the Feast definitely demands a steep tax... over and over and over.
But there may be times when it provides no real problems. Are there decks that have small creatures that don't fly... and also don't play much creature removal? Master of the Feast may shine when the opponent can't really interact (and therefore can't really take advantage of its downside), perhaps as a sideboard card.
Because it is in black, we can also use Duress and Thoughtseize to mitigate the card economy issues; we might not be able to keep the opponent from drawing, but maybe we can take away the cards we care about, still.
But yeah... this is a tough one.
It's not a whiz-bang "play me!" but, at the same time, when I asked how much was fair for a 5/5 flier... I don't think very many of us had three in mind.