Arcane Duelist

It was somewhere between the creation of the universe and the time Iggwilv gave Mordenkainen a magic swirlie that drowned hundreds, that John Cobble decided to learn magic.  After he changed his name to Ace Quickcast he developed a magic style that was all about breaking the conventional laws of magic.  After his ironic death to a textbook about the fundamental laws of magic, people discovered his life's work: the Arcane Duelist.

"Never do the heavy lifting while practicing magic, it works for you and you tell it what to do" -Ace Quickcast.

Fast Casting

You can cast any cantrip you have prepared with a casting time of an Action as a Bonus Action.  When a creature provokes an Opportunity Attack from you by leaving your reach, you can take a reaction to cast a cantrip targeting that creature rather than making an Opportunity Attack.

"The question isn't Fireball or Fire Bolt, it's Fireball and what else" -Ace Quickcast, guest lecturing.

Focus Fire

You prioritize the monsters that are the most threatening.

When you cast a spell, if one or more creatures would be damaged by it you can choose one creature affected by the spell.  You can alter the spell so that creature is the only creature affected by the spell, but the spell does maximum damage.  You can alter spells in this way a number of times equal to your Intelligence modifier, and regain all expended uses when you finish a Long Rest.

"It's not like how many of them their are matters so long as the strongest are dead" -Ace Quickcast, fighting wolves.

Quick Draw

You can react to an attempt at casting a spell and prevent it.

When a creature you can see attempts to cast a spell, as a reaction you can choose a spell you know that requires a saving throw and has a range equal to or greater than the distance between you and the creature.  A spell slot of the chosen spell's level is expended, and the creature must make a saving throw of the same kind required in the chosen spell DC 8 plus your Proficiency Bonus plus the level of the spell slot expended.  On a failed save the target's spell fails and has no effect, and the Action, Bonus Action, or Reaction used to cast it is wasted.

"Your one mistake: you thought you were faster than me" -Ace Quickcast, duel winner.

Dueling Stance

You assume a dueling stance, focusing on your target and sealing their fate.

At the beginning of your turn you can assume a dueling stance, reducing your speed to 0 and giving you the following benefits until the beginning of your next turn:

Surefire.  You have advantage on all ranged spell attacks.

Double Tap.  If you cast a Cantrip as a bonus action you can cast another cantrip immediately after (no action required).

Focused.  You can use Focus Fire without expending a use of it.

Powerful Draw.  The DC of your Quick Draw increases by the level of the spell the target is casting.

"I  will make my last stand here and now.  I might not make it, but I know for sure you won't" -Ace Quickcast, the Battle of the Library.