The fighter is the meat shield of the group. He's supposed to take damage and deal out melee justice, however the first role is the most important one (note: I'm debating between calling this class fighter or warrior as both represent very similar ideals, so sorry if I've interchanged the names in previous post, we're going to call it fighter for now).
Trait 1: Pay 1, intercept one attack directed at another player (spell, ability, or regular attack) and make the target of the ability this fighter. All effects and damage are calculated as if the fighter was the original target of the attack. Can be used once per round as a free action.
Trait 2: Reduce damage taken by this fighter by 1 for every defense point sacrificed. This can be used at will.
With this setup, it is clear that the warrior is all about buffing his defenses and intercepting attacks. He is the meat shield and the tank of the group, soaking up damage, and letting the priest heal him and the rogue and wizard deal damage. It wouldn't be unusual for him to make a melee attack just to give the rogue his flanking bonus. The fighter works best when there is one or two targets, as he only gets one trait intercept per round, but has other cards that can work similarly.
Take the Hit
Instant - Can be played at any time.
Effect - Counter one attack (spell, ability or regular attack) that would strike an ally. Resolve the attack against yourself instead.
Effect: Counter one regular attack made against you this round. Make a free basic attack against that enemy.
Effect: At the start of your turn gain 2 block. Your attack is reduced by 2 and your defense is increased by 2 while this card is in play.
The Art of War
Effect: Discard this card. Put one Tactic into play, tapped.
Effect: You gain 5 block.
Effect: Increases your attack by 2 while this card is equipped.
The downside to fighter is that while he has a lot of good defensive abilities, most of them prevent him from becoming a powerful offensive weapon unless he has help. As seen in the play test, after getting buffed by both the wizard and the priest, he was able to dish out a lot of hurt and stay safe himself. He is very reliant on team support, but once he has it he is nearly unstoppable.
The fighter's greatest weakness is the lack of any spell resistance. Spells will rip right through his health quickly, and while he can use block to reduce the damage, it will eat through this secondary resource very swiftly. This means he has to be selective about the damage he takes and the abilities he intercepts. It might hurt the wizard more to take a sword to the face, but a lightning bolt is another matter. The fighter's player must be aware of the entire situation, and play accordingly.