Curse Deeply

This spell is a twisted version of the wish spell, and it can only do negative things (create undead out of the living, inflicting lycanthropy/vampirism onto someone, giving an enemy disadvantage on everything, etc.). Ironically, the wish spell is the only spell powerful enough to undo its magic. As with the wish spell, wording is key. There is also a chance (likelihood determined by how precise the wording is) that the effects may backfire, and target you instead (unless you were for whatever reason the intended target, in which case anyone other than you could receive the spell's effects).

The stress of casting this spell to produce any effect weakens you. After enduring that stress, each time you cast a spell until you finish a long rest, you take 1d10 necrotic damage per level of that spell. This damage can't be reduced or prevented in any way. In addition, your Strength drops to 3, if it isn't 3 or lower already, for 2d4 days. For each of those days that you spend resting and doing nothing more than light activity, your remaining recovery time decreases by 2 days. Finally, there is a 33 percent chance that you are unable to cast Curse Deeply ever again if you suffer this stress.