Conjure Blood Mass

Transmutation Cantrip (Sorcerer, Warlock, Wizard)

Casting Time: Reaction, which you take when a creature in range takes slashing, piercing, or necrotic bleeding damage
Range: 60 feet
Components: V, S
Duration: 10 minutes

When a creature within 60 ft of you takes slashing or piercing damage or necrotic bleeding damage you may use your

A Reaction is a special action taken in response to a trigger defined in the Reaction's description. You can take a Reaction on another creature's turn, and if you take it on your turn, you can do so even if you also take an action, a Bonus Action, or both. Once you take a Reaction, you can't take another one until the start of your next turn. The Opportunity Attack is a Reaction available to all creatures. See also Opportunity Attacks and Actions.

to shape its shed blood into a floating mass usable for hemomancy spells. In order to shape a blood mass it must have lost at least 5 HP from a slashing piercing or necrotic bleeding damage source. These blood masses then float towards then orbit near you ready to use.

After 10 minutes, the blood stales and becomes unusable and falls to the ground.

Cantrip Upgrade: The number of blood masses you can conjure increases when you reach levels 5 (2), 11 (3), and 17 (4).

Source: Champion's Ascension