Red Wizard of Thay

 By joining the ancient tradition of Thay, you specialize in a school more than any other wizard, you tattoo arcane magic onto your skin. Using your arcane might to empower your specialist school. Using the power of circle magic, your allies can donate their power to increase your own. A powerful Red Wizard can make his enemies outright fail saving throws from his chosen school

 This subclass is from the amazing Red Wizard Handbook by RP Davis, please consider this incredible resource to really flesh out your Wizard!

School Specialization

When you take this tradition at 2nd level you must select two schools of magic. One of these is your Favored school, the other is your Forbidden school. You can’t cast spells from your Forbidden school, and you can’t write them into your spellbook, either through increased wizard level or through copying spells you find. You can copy spells of your Favored school into your spellbook as if they were your own (1 hour and 10 GP per spell level).

Tattoo Magic

Starting at 2nd level, you know how to scribe a magic tattoo on yourself. You can tattoo yourself with 2 spells from your Favorited school. Tattooed spells are always prepared for you. Once you choose these spells, you can't change them later. You can tattoo an additional spell at 7th, 11th, and 15th level. When you scribe your first Magic Tattoo on yourself, you also gain proficiency in the Intimidation skill if you don’t already have it.

Empowered Specialization

When you reach 6th level, when you deal damage with a cantrip from your Favored school, you can add your Intelligence modifier to the damage roll (minimum 1). In addition, when you cast a spell from your Favored school that forces a creature to make a saving throw, you can impose a disadvantage on the saving throw of a single creature affected by the spell. If the spell requires you to make a spell attack roll, you can grant yourself an advantage on the roll. Once you use this ability you can't use it again until you finish a short or long rest.

Circle Magic

Beginning at 10th level, you can lead a number of friendly arcane spellcasters in a Circle. When you use an action to cast a spell, any number of friendly creatures within 30 feet of you up to your Intelligence modifier (a minimum of 1) can use their reaction and expend a spell slot to increase the level at which you cast your spell. This can increase the level of the spell beyond what you have spell slots to cast normally, but can't exceed 9th level. For example, a 5th-level Red Wizard casting fireball uses Circle Magic with 2 other 5th-level casters, each of whom donate a 3rd-level spell slot. In this way, the Red Wizard can cast fireball as though she used a 9thlevel spell slot

School Zulkir

Starting at 14th level your mastery over your Favored school is complete. When casting a spell from your Favored school, if the spell offers a saving throw, you can decide that creatures affected by the spell automatically fail the saving throw. If the spell requires you to make a spell attack roll, you can decide you automatically hit. Once you use this ability you can’t use it again until you finish a short or long rest. A creature with Legendary Resistance must expend two uses to choose to succeed on this saving throw instead of failing. If they only expend one use, they make the save at disadvantage instead of automatically failing.