Blood Magic

Using this feat when a creature dies by your hands, you may siphon the magic from their blood augmenting your next spell. When you reduce a creature to 0 Hit Points and it dies, as a part of that same action you may draw out its blood and absorb it into your body, if the creature is an Undead, a Construct, or a creature summoned by magic nothing happens. Until the end of your next turn you gain a temporary spell slot, the level of the slot is based upon the Level or CR of the creature. 

  CR          Character Level          Spell Slot Level

  0-2                     1-4                                  1

  3-8                     5-8                                  2

 9-14                   9-12                                3

15-20                13-16                                4

   21+                  17+                                 5

If you reduce a creature to 0 Hit Points and it dies, that isn't an Undead, Construct, or a creature summoned by magic, as a part of a ritual casting of a spell the extra time to cast the spell is 1 minute instead of 10 minutes.