Life Caster

You can cast the spells you know and/or have prepared by expending a number of Hit Dice equal to the spell's level. For each Hit Die expended in this way, you take necrotic damage equal the roll of the Hit Die plus your Constitution modifier, this damage cannot be reduced in any way.

You can cast a spell at a higher level by expending additional Hit Dice per level of the spell, you can only cast spells up to the highest level spell slot you have.

You can only cast spells at 6th, 7th, 8th, and 9th levels once each, and you regain the ability to do so after completing a long rest.