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Ok, in this article, I felt I would outline what (as it seems to me) is the standardized cost formula for most creatures. I do have a purpose for this as well, which will become obvious after the basis is set up.

Vanilla creatures:

1 colorful gets you a 1/1 with no abilities but perhaps a usable creature type (like goblin)
or a thoroughly mundane ability.

1 colorful and 1 colorless gets you a 2/1 (again, with either a usable creature type or
mediocre ability) or the classic grizzly bear, a 2/2

2 colorful will almost invariably make the critter a 2/2 and give him an almost
worthwhile-to-spiffy ability, or maybe a couple mid-range ones.

1 colorful and 2 colorless usually nets you the standard grey ogre sized critter (2/2) and
an ability, sometimes even a decent one at that.

This usually progresses on with each colorless mana equaling 1 toughness or 1 power, or
1 fair to middling ability; and each colorful mana equaling either a power and a
toughness, or one or the other and a medium ability.
Wind drake, kris mage, and trench worm fit this bill in my book.

Icky Liver creatures:

Very similar to the Vanilla creatures, but usually with a colorless mana tacked on, and having a greater tendency towards the usable creature type rather than a generically playable ability. Grey ogre, hill giant, lots of the kavu (like the ancient kavu), and many others are good examples of this.

Tasty chocolate chip creatures:

As Vanilla, but minus a colorless mana, or with a highly useful ability or combination of abilities that was heretofore unwarranted…
Morphling, masticore, river boa, and several others go in this box.

And now for the point… bog gnarr? What on earth? I hate seeing garbage like this. I understand the need for flak creatures, but this goes below and beyond the icky liver variety. It costs 2 colorless mana too much. Not only is it's ability not good enough to warrant costing one extra mana (let alone 2), it isn't even a creature type of note (even if it was a kavu goblin rebel this guy wouldn't be playable). Him and all those like him (and you know you're a bad creature when I rank pyknite above you) have no place amongst the reasonable ranks that we call the flak creatures. Go back to your bog, I like your cousin the glade gnarr far more, and glade gnarr is still not constructed worthy (but at least you can convince someone else to burn a counter on your turn before you attack to pump the glade one…).

And, since I'm on the subject of bad cost relations, blue itself should have a 2/2 flying guy for 2 blue, red should not have to pay an extra colorless on it's firebreathing critters, and black and green should be not be charged the normal extra colorless for their regeneration abilities. (*looks at drudge skeleton and pygmy pyrosaur meaningfully*).

There is a thin line between flak and unplayably bad. Please, in future, try not to cross it.