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. You can have only one homunculus at a time. If you cast this spell while your homunculus lives, the spell fails.

When you finish a long rest, you can spend up to 1/2 your Hit Dice to boost Homunculus' HP (if on the same plane). Roll each die and add your Con modifier. 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 your HPs no lower than 1 HP, and the change to both your HPs ends when you finish your next long rest. The reduction to your HP maximum can't be removed by any means before then, except by the homunculus's death.