It's a pretty state-forward win Strategy: control the board with spells and dragon synergies during early, and mid-game. Trade on value and use Galankrod's hero power to outlast the competition. If you enjoy playing control with a good amount of removal spells, this deck is worth a try! The deck also holds up it's own on minions, which makes for a great board presence and value trading experience.
Mulligan: Cleric of Scales (keep a dragon if you have one), Card NameRelinquay of Souls, Dragonmaw Sentinel, Penance, Mindflayer, Shadow Madness. (keep Sethekk Veilweaver and Renew if nothing else good and you're facing aggro. Sethekk can be used as a 2/3 on turn two if in a pinch, but it's better value used later on).
*Note: I've seen other Dragon Priest decks trying to get the most out of Galankrod with invoke minions, and this deck is a different take. I see Galankrod's value as a strong one-minion removal and the ability to add to the board late game. That and the synergy with Kronx. You won't need the extra invoke minions in the early and mid-game, and you have plenty of other forms of removal to lean on.