Druids love nature and will often do anything for it. Generally, they are a goodly class of beings. However, not all are. An Antidruid is someone who was wronged in some deep way by a druid, in a way so deep it opened up an inner power they didn't know existed.

As the most grave insult to a Druid's power, they instead drain life to power their spells. When it first started, they would have noticed an innate ability to cast spells, but when they cast, nearby plants would wilt and small animals would sicken in their vicinity. As they developed their powers further, they would notice the larger the spell, the more damaging the spoils. 

Anti-life Magic

 

When you cast a spell, it requires life force. The lower the level of spell, the lower the cost. If you have spell slots, you may use those (but you don't get as many as a "normal" sorcerer). If you cannot, you must siphon life from something nearby to cast anything above the level of a cantrip. 

Casting a cantrip will make others around you feel a momentary sense of nausea. Any other spells will wilt any and all non-magical plant life in a radius of 5 feet per spell level. If that radius doesn't at least have full coverage, life will need to drain from elsewhere. You can drain this life from yourself at a rate of 1d4/spell level or from a willing participant at 1d8/spell level. Finally, you can do temporary damage to your CON score, with a minimum cost of 1, at a rate of 1 per 3 spell levels of casting. 

 Any CON damage caused by the use of this feature is healed on a long rest.

Well of Anti-Life

Your maximum CON score and current CON score are increased by your Proficiency Bonus.

Antipathy

Once per short rest, you can declare a spell and reach out and attempt to siphon life from another individual. The target must make a WIS save against your Spell DC. If they fail, do damage to their CON equal to the cost required to cast your spell. If they succeed, you still cast the spell, but at a cost to your own CON.

Anti-limitations

At 14th level, you gain a modicum of control over your ability to drain life. If there is no life in your immediate drain-life area, you can extend the circle by a number of 10-foot radials to still be able to cast (costing double what you normally would). This maxes out at a 1-mile radius. 

Also, you are able to now sense life in a 500-foot radius. You can only feel a general direction and distance, but not the type, size, or number of the life force. 

Antibody

Beginning at 18th level, you gain the ability to become an avatar of death. For one minute, your form darkens to almost a three-dimensional shadow, writhed in red lightening. You still take all damage as you normally would.

Upon use, any CON damage you have is healed completely. Also, for the duration, you become resistant to CON damage, specifically. 

Once per turn, as a bonus action, you can send out a pulse of anti-life energy, causing all creatures within 15 feet of you to roll a WIS save. Any who fail take 1D4 CON damage. Any who save take no damage and are immune to this effect for 24 hours. Any CON damage dealt by this feature is healed upon a long rest.