For all their intelligence, some wizards can be rigid, hard-nosed adherents to tenets or misconceptions about magic, the planes, and the various denizens each produce. For many hundreds of years throughout most realms it has been accepted that goblinoids were subhuman, worthy only of extermination like a particularly fast-breeding dangerous species of vermin. It is still common knowledge that fiends are inherently evil, not to be trusted, and best to be avoided or slain if at all possible. Often influenced by religious zealotry, there are wizards who take such knowledge to extremes, and set upon a path to carry out exterminations of what they deem to be intolerable threats to civilization. They view their butchery as abattage, the slaughter of sick, diseased or virulent creatures to prevent it spreading to others.

Elves of the Eldreth Veluuthra sect in Faerun count several anti-human Abattagists among their ranks, while the Witches of Rashemen have sought the services of anti-undead specialists in their defense against Thay, and anti-fiend Abattagists are not unheard-of anywhere in the realms - though they tend not to be long-lived when they attempt to exterminate such challenging opponents, and instead try to deal with fiends more through management and containment. Abattagists may view their actions as 'good' or 'necessary' but rarely characterize themselves as 'evil' though their methods may cross generally-distinct moral boundaries. 

Studious Martial Fervor

With cultural and religious zeal, you seek to preserve your civilization against species you perceive to threaten extinction of your way of life. Beginning at 2nd level, you can learn spells from the Paladin spell-list. These count as wizard spells for you and use Intelligence as your spell-casting ability.

Further, with knowledge that violence is a necessary tool to abattage, you have learned to cast spells with somatic components even while your hands are otherwise occupied with weapons or other items. You gain the War Caster feat (PHB p170).

Lastly, you have of course declared one species to be your enemy - studied their history, nature, language and culture - and you despise them utterly. You learn one language of your Favored Enemy (like the Favored Enemy of Rangers, PHB p91) and have advantage on intelligence-based skill checks to recall information about them.

Practiced Slaughter

At 6th level, your study of the enemy's anatomy, tactics and mindset grant you special knowledge of how to more swiftly bring about their demise. You have advantage to all spell-attacks against your Favored Enemies. Additionally, when specifically targeting one or more of your Favored Enemies, you add your proficiency bonus a second time to your spell-save DCs. This is target-specific, so area-effect spells do not again this bonus.

More Threats To Kill

At the mid-point of a career of slaughter, there may come a re-prioritization of where the true threat lies. At 10th level, you commit yourself to studying the language, culture, history, lore and nature of another Favored Enemy. You retain all knowledge and bonuses against your old enemy, but have identified another threat you are prepared to exterminate. 

Never Let Them See It Coming

At 14th level you predict and anticipate the actions of your Favored Enemies, adding your Intelligence modifier to your initiative roll in combat against one or more of your Favored Enemy. Additionally, any weapon or spell attack against one or more of your Favored Enemies is a Critical Hit if that creature hasn't taken its turn in combat yet.