Well, this has become one of the more popular K&C decks. Since I am F2P mostly I took practically all dragons I have atm (which means yes, no Drakonid operative), but have netherspite historian for value.
As with all big spell dragon priests, spiteful summoner uses both mind control and free from amber for large board presence, even though I have only 1 spiteful summoner, but compensate it with faerie dragon, ironbeak owl and acidic swamp ooze for situational matchups.
As you can see this deck is chock-full of silence minions which is bane of cubelocks. Vs aggro you want to get duskbreaker asap and owl in canse aggro paladin has many divine shield minions.
As for mulligan, I usually go to cleric, shadow ascendant and tar creeper, but in case I get initialy any dragon, I try to keep it, as to maximize potential duskbreaker/historian early in the game.