Hearthpwn

Latest version of a promising spell-oriented priest with elemental synergy.

Rather than taking a 100% control or OTK deck approach, this deck attempts to fight for the board with elemental minions until Lyra the Sunshard is either played or discovered via Servant of Kalimos. It is fairly easy to put down an elemental on turn 4, especially Lightspawn.

Once Lyra is down (hopefully with at least one Radiant Elemental in place), cast as many spells as possible, since each spell will generate a new priest spell in its place.

In particular, it is helpful to buff Lyra's health or heal taunt minions to protect Lyra, as the next turn can easily become a spell fest. You can never run out of spells to cast so long as Lyra lives and you have targets. You may be able to create a giant minion for OTK, but with significant board presence you may only need a few spells to tip the scales permanently in your favor and win the day. It is also helpful to have Priest of the Feast on board during the casts if your hero needs healing.

Some alternate cards to consider:
Arcane Anomaly
Binding Heal
Crystalline Oracle
Shadow Visions
Violet Teacher
Blazecaller
Medivh, the Guardian

Have fun and offer your feedback in the comments. Give it an upvote if you like the deck!