When you take this feat, you may use Constitution as your spellcasting ability instead of your current spellcasting ability. If you have multiple spellcasting abilities from different classes, you must choose one. Taking this feat multiple times allows you to choose another classes' spellcasting ability to change.
Additionally, you may cast spells using your hit dice instead of spell slots. When you cast a spell, you may expend hit dice equal to the spell's level minus half of your constitution modifier instead of any spell slots. When you expend these hit dice, instead of healing you take damage equal to the result.
Note: Based on my Bloodheir Subclass I made a couple years ago. I thought all classes should have the ability to do blood magic if they wanted to, so I made this and one other feat. Also, there is no official way to make a feat change your spellcasting ability on character sheets, so you'll either have to make a private homebrew of the subclass you're using and change the spellcasting ability to constitution or just keep track of that stuff manually.
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