Nature's Boon
I think it would be better cc'ed at 1G, but I think it's not too powerful at G. At any rate, this card is fun.
Badge of Honor
Isny prasmatic lace, that card that does 1/3 of what this does, 1W? I suggest WW.
Traitorous Giant
Looks good, except the control cost of R. I think thats too low; it gives the owner of the card way to much control of the giant if the oppenent dosent have access to red. I suggest RR.
Temporal Armor
I compare this to Dense Foilage, the 2G card that prevents all creatures from being target by spells. The Armor protects just your creatures, and from abilties to. To boot, it's an unsummon seal. All this for just a conversion of 1 to U seems to powerful. I suggest a cc of 3U, or a cut of the unsummon seal ability.
Karmic Balance
I dont know about the power; I cant tell. A suggestion about rulings though; maybe for each ability you should say 'The Player with the lowest life when K.B. came into play"
It seems very confusing to me.
Essence Siphon
Somewhere Duke mentions that he likes the life loss aspect of this card....but I dont see any. Was your intention "You gain life and your oppenent loses life equal to the casting cost of that permanent" ?
Also, maybe it should be "non-land, non-enchantment" because black never has a way to deal with enchantments. I like the card as is, with the enchantment sacrifice....
Anyway...tell me what you think.