Cancer mage

School of Viromancy

Plague Host

Beginning when you select this school at 2nd level, you become immune to the ill effects of all diseases, other than purely cosmetic ones such as: boils, pockmarks, watery eyes, blackened skin, hair loss, foul smell, and so on. 

You become a carrier of every disease or poisoning effect you encounter, you gain resistance to poison and necrotic damage

However, should You be the target of a spell of Greater or lesser Restoration, you take 1d6 Damage per spell level and temporarily loose all of your Viromancy School abilities until taking a long rest.

Plague Bearer

At 2nd Level you gain the ability to weave disease into your spell work. you gain a pool of disease points equal to two times you proficiency bonus. Once per turn, when casting a spell of 1st level or higher, you can choose to expend on of these points to make this spell contagious. That spell does, starting at 2nd level, 1d6 extra Necrotic Damage on hit; raising in damage per caster level as seen in the plague bearer chart.

This skill does not effect constructs, the undead, or creatures immune to poison.

Cancerous Companion

Starting at 6th Level, You grow a Large Cancerous Tumor somewhere on your body. This Tumor acts a Special Familiar. With a seperate personality and Mirroring your stats at your current level

You and the tumour may communicate telepathically. The tumour cannot be dismissed nor may it occupy any other space other than your own. If the You are Ever brought under the effects of a Mental Condition which gives disadvantage or loss of control (Example: Fear, Charm, Unconscious) You may as a reaction switch to the tumor's persona and Ignore the Condition.

Viral Thrall

Starting at 10th level. after hitting someone with your Plague Bearer skill you may choose to expend an additional plague point to attempt to sicken your target. Using your spell save DC, on a failure the target gains a disease. Your control over Viromancy is becoming so great that you can bend them to your will, after successfully infecting a Creature with a disease, once per long rest you may as a bonus action force the virus in that infected person to do your bidding, controlling the infected creature as if using the Dominate Person Spell without the use of a spell slot

The Dominate Person, as well as all contagion effects are completely reversed by the lesser/Greater Restoration Spell This skill does not effect Undead or Constructs or those Immune to Poison

Disease form

At 14th Level, you gain the ability to take the form of a disease once per day (This ability also effects up to 100 Lbs of your gear and items. As a Disease You are intangible and Invisible to all standard methods of observation. Though creatures with high Perception (smell) may note a foul scent to the air. You cannot move from your Space as a disease except by Wind or Host. You may adopt your Disease form as a standard action. Intending to infect a living creature within 10 feet of you.

The Creature you attempt to infect must make a Constitution roll against your Spell Save DC. On a successful save they becomes immune to your contagion for 24 hours On a failed saving throw you take control of that creature. Acquiring their skills and stat block.

The Infected Creatures Maximum Health is Halved Every Day You Infect them. Gaining One level of Exhaustion as shown in the Dungeon Masters Guide Until their Health Pool Reaches 0, killing them.

A Greater Restoration Spell cast on the Infected creature or area of your disease form does 2d6 Damage per spell level You are ejected from the host. and it takes 24 hours for you to reform into your human shape. Your abilities are Locked until you can then take a long rest. 

If the host dies outside of by a greater restoration spell, you are ejected and reform into your normal form instantly. Becoming unable to do this ability again for one week.

This skill does not work against Creatures Immune to poison, are Undead or Constructs