Pilestedt says the first thing the testers tried to do when playing PvP is spam ice shards -- an effective technique that dominated opponents consistently during early testing. Thankfully, that's been balanced; the more ice shards a player casts, the less damage they deal proportionately. Additionally, damage is also tied to velocity, so the longer a player charges the ice shards, the more damage they will deal, which hopefully will provide players with incentive not to spam.
Other changes talked about involve beam projectiles and defensive auras, both of which have been tweaked considerably: beams now have a potential to damage the caster. Before, if a player cast a shield and another player cast a beam, the beam would explode when meeting the shield and knock back the shield caster. Now, the blowback affects the caster; one must be careful when deciding to cast a beam, lest they injure themselves. And as for auras, they now offer full protection from any spell using that element.