While speaking an intricate incantation, you cut yourself with a jewel-encrusted dagger, taking 2d4 piercing damage that can’t be reduced in any way. You then drip your blood on the spell’s other components and touch them, transforming them into a special construct called a homunculus. The statistics of the homunculus are in the Monster Manual. It is your faithful companion, and it dies if you die.
Whenever you finish a long rest, you can spend up to half your Hit Dice if the homunculus is on the same plane of existence as you. When you do so, roll each die and add your Constitution modifier to it. Your hit point maximum is reduced by the total, and the homunculus’s hit point maximum and current hit points are both increased by it. This process can reduce you to no lower than 1 hit point. and the change to your and the homunculus’s hit points ends when you finish your next long rest. The reduction to your hit point maximum can’t be removed by any means before then, except by the homunculus‘s death. You can have only one homunculus at a time. If you cast this spell while your homunculus lives, the spell fails.