So I was reading through the blurb in Mordenkainens Tome of Foes about Abishai I got to thinking about how I could allow a player to become an Abishai. I chose to start with Wizard as the base with the view that Blue Abishai specifically state their spells are from the wizard list and the other abilities they have can be achieved through multi-classing options: Black Abishai are more sneaky/infiltrators so some form of rogue would be a likely option, although I also thought Ranger as the Abishai have no sneak attack abilitiy. Green Abishai state their spell casting is Charisma based so i thought Sorcerer for them, I ruled out Bard due to the innate spells Green Abishai have not appearing on the bard list. Red Abishai are leaders and seem to have a few "paladin-esque" powers and White Abishai have some very Barbarian like abilities.

So all that said I did a little poaching from other subclasses and cobbled together the below, it also doubles as a "secret" society for DM/NPC use.

All comments, suggestions or critiques welcome.

I'll try to make it available through D&DB but it currently insists its to close too the Druid Circle of Spores (?!?) so until I fathom out whats going on with that I present to you.......

Wizard subclass: Abishai of Tiamat

In order to start down this path of Wizardry you must be Lawful Evil in alignment and should you become a non-evil alignment you cannot pursue this class further until you become evil aligned again.

Abishai of Tiamat are a semi secret society of Wizards dedicated to freeing Tiamat. Some wizards are approached by fiends called Abishai at Tiamats behest and given a task or quest, if they are successful they gain Tiamats blessing and are inducted into the society, the Abishai then becomes the Wizards mentor.

The Abishai of Tiamat hope to please Tiamat and attain her favour and actually become one of her Abishai in the Nine Hells.

Most Abishai of Tiamat multi-class in order to fully emulate the colour of Abishai they are mentored by, many sell their souls to Tiamat and become Warlocks (Fiend but any pact) or take training to emulate their Abishai Mentor and also display certain aptitudes (ability scores/classes) of their mentor as noted below, although strangely those following Blue Abishai mentors often retain a purely Wizardly role.

All Abishai of Tiamat are expected to learn the spell Contact Other Plane as soon as they are able to cast 5 level spells (take as one of their level up spells) and contact one of Tiamats envoys, this is considered a matter of etiquette and failure to do so may cause Abishai to be sent after the errant wizard.

ABISHAI MENTOR (lvl 2)

At level 2, choose one type of Abishai as your mentor, this is the colour of Abishai that contact you and started you on your way to learning about, and serving, Tiamat. The damage type associated with each Abishai is used by features you gain later.

You also learn to speak, read, and write Draconic and Infernal.

TIAMATS BLESSING (lvl 2)

Also at level 2, Tiamats blessings flow through your veins, it causes physical traits of your Abishai mentor to emerge. At 2 level your hit point maximum increases by 1 and increases by 1 again whenever you gain a level in this class. Additionally, parts of your skin are covered by a thin sheen of dragon-Iike scales.

When you aren't wearing armour, your AC equals 13 + your Dexterity modifier.

As you gain levels in this class you gain certain cosmetic physical changes to your appearance and gradually come to resemble an Abishai, such changes may include, but are not limited to: face becoming more “dragon-born” in appearance, teeth turning into fangs, the growth of a dragon like tail, claw like finger and toe nails or a change in skin colour. Any changes are purely cosmetic and do not grant any additional abilities, modes of movement or attack.

Additionally, your size changes to medium if you are not already medium sized.

ABISHAI AFFINITY (lvl 6)

At level 6, You gain resistance to the damage type associated with your Abishai mentor.

ABISHAI WINGS (lvl 10)

Ar level 10, You sprout a pair of wings akin to dragon wings. You gain a fly speed equal to your normal walking speed. Any armour or clothing you wear will need to be custom made to account for your wings.

EYES OF TIAMAT (lvl 14)

At level 14, Your eyes become infuse with Tiamats power and you gain Devil Sight as per the Warlock Invocation. If you already possess Devil Sight, or subsequently gain it, the range of your devil sight increases from 120ft to 150ft.

Huh so earlier edition Paladins being restricted to being only Lawful Good, correct?

not sure about 4e D&D but 3.5e and earlier had a strict LG alignment restriction for paladins but 5e has no such problem, I think Oath of Conquest or Vengeance would porbably be the best fit for the Red Abishai multiclass if you were going to go for it

Quote from Rob76 >>

not sure about 4e D&D but 3.5e and earlier had a strict LG alignment restriction for paladins but 5e has no such problem, I think Oath of Conquest or Vengeance would porbably be the best fit for the Red Abishai multiclass if you were going to go for it

 Maybe even war domain cleric. 

I steered away from Cleric domains as the red abishai has a couple of "aura" typr effects (Frightful Presence and Incite Fanaticism) that were closer thematically to those granted by the Paladin, but then again, the idea with the class was to gaun knowledge of Tiamat and win her favour and becoming one of her clerics to weild both arcane and divine magic in her name might be something that would get a potential follower that much close to attaining the role of Abishai.

Quote from Rob76 >>

I steered away from Cleric domains as the red abishai has a couple of "aura" typr effects (Frightful Presence and Incite Fanaticism) that were closer thematically to those granted by the Paladin, but then again, the idea with the class was to gaun knowledge of Tiamat and win her favour and becoming one of her clerics to weild both arcane and divine magic in her name might be something that would get a potential follower that much close to attaining the role of Abishai.

 Yeah. I just thought since their basically loyal to a specific god, it would make sense to multiclass with a cleric.