School of Shitmancy

As a result to your inability to acquire proper casting materials, or maybe because of a weird fetish or character deviations, your magic has becomes associates with that which is normally ignored by other wizards: shit.

The vileness and putrefaction effects of this magic are not for all, only those with higher physical resistance are able to withstand the horrid smells and unappealing looks of this magic. All of those nights on the toilet due to food poisoning and disease have made you tough in ways others cannot imagine. Still, there is much power in transforming mere excrement into something as powerful as a golem or a destructive shit ball. Yes, it is ugly, but you have accepted that and grown beyond what the eye can see and noses can feel. 

While mages of other schools may look at you with repugnance, you respond back with derision, as it is very easy to bring wonderful magic from pearls, diamonds, etc. No matter how they try, they cannot master the mystery of your art. Shitmancy spells are specific to this class and cannot be learned without the physical pain and suffering required to do so.

Mechanically, shit is treated as poison damage.

Shitmancy Savant

Beginning when you select this school at 2nd level, the gold and time you must spend to copy an shitmancy  spell into your spellbook is halved.

Horrific Spells

The sight of your fetid magic disturbs the inner working of others who witness it. When you successfully cast a shitmancy spell that affects other creatures, you can choose a number of creatures within 30 feet of the target equal to your constitution modifier (minimum of 1). The chosen creatures automatically have disadvantage in their saving throws and attacks until the end of your turn. Impacted creatures ignore damage resistances and take half damage if they would normally take no damage on a successful save. This only works if the other creatures are able to see or smell the effects of your magic.

And It All Went to Shit

You can transmute any spell you cast to count as a Shitmancy spell and benefit from any additional benefits and traits from conjuring spells from that school that you may have, such as the "Horrific Spells" trait.

Natural Immunity

Beginning at 10th level, you have resistance to poison damage, and you are immune to diseases. You have spent so much time dealing with diseases and parasites and the that you have become inured to some of their worst effects.

Plague Bringer

Your magic initiates a chain effect that can spread through small regions.

When you deal shit damage with an attack or area effect spell, you can choose to deal an additional quarter of that damage to creatures of your choice within 20 feet of the original target(s). This damage ignores resistance and immunity.