Thunder Surge is a powerful growth spell, with the potential for devastating amounts of damage. While it can deal as little as 2 damage, it can potentially deal a dispersed 30 points of damage to a full battlefield.
Target unit, and all units connected by adjacent units, take 2 damage.
Thunder Surge is often used to counter creature-heavy decks.
Thunder Surge's behavior is referred to as "targetArea": "SEQUENTIAL" in the game's code.