Conjure parasite weapon

You conjure up either a rapier, dagger or arrow of bone, flash and keratin, that you can then use as said weapon. On a hit, the target takes appropriate damage for said weapon and the weapon is then stuck in the target. Anyone can try to remove the weapon with a strength check against your spell save DC. If the weapon is successfully removed before your next turn the weapon disintegrates. On your next turn the weapon starts spreading in the targets body causing  1d4 piercing damage. On each of your turns for the duration the weapon does another 1d4 piercing damage. If the weapon is removed with a strength check after the spread of the weapon the target takes slashing damage equal to 1d4 for every turn of the weapons spread. If the caster losses concentration on the spell the weapon disintegrates doing no further damage. The weapon can also be safely removed with 3 successful medicine (intelligence) check against the casters spell save DC.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the initial damage increases by 1d4 for each slot level above 1st.