Tweaks
Standoff: Killing enemies grants a stacking buff to reload speed and weapon accuracy/recoil reduction. Rapidly decays over two seconds of not getting kills.
Gunslinger: Dealing damage increases weapon swap speed and secondary weapon damage. Buff is consumed when not dealing damage for five seconds, or when firing your secondary weapon.
Spells (All have high CD to account for effectively being extra weapon slots)
Duel (starting spell): Mark the enemy in your crosshairs. It takes extra damage (30%? 50%?) for three seconds. Fast cast time.
Quickdraw: Rapidly fire six accurate bullets from a spare revolver.