Blood to Acid

Make a melee spell attack roll against a creature. On a hit the targets blood begins to turn to acid burning them from the inside. The target takes 3d6 + 1d6 for each time this spell has dealt damage to the target, Acid damage at the start of their turn. Each turn that the spell remains in effect and deals damage to the target the effects of the acid become more and more severe.

First time it deals damage, the target has disadvantage on concentration checks until the start of their next turn.
Second time it deals damage, the target makes attack rolls with disadvantage until the start of their next turn and all previous effects. 
third time it deals damage, the target must make a Constitution save against your spell save DC or drop anything they are holding and all previous effects. At the end of their turn the target makes a Constitution save ending this spell on a success.
Fourth time it deals damage, the target's speed is reduced by 10ft until the start of their next turn and all previous effects..
Fifth time it deals damage, the target makes all saving throws with disadvantage until the start of their next turn and all previous effects..
The Sixth time it deals damage, the target can't cast spells or use reactions until the start of their next turn and all previous effects. At the end of their turn the target makes a Constitution save ending this spell on a success.
Seventh time it deals damage, the target must spend their action flailing and screaming and all previous effects.
eighth time it deals damage, the target is blinded until the start of their next turn and all previous effects.
Ninth time it deals damage the target becomes vulnerable to all damage until the start of their next turn and all previous effects . At the end of their turn the target makes a Constitution save ending this spell on a success.
Tenth time it deals damage the target becomes paralysed until the start of their next turn and all previous effects.

If you end your turn without line of sight to the target or if you are more than 120ft from the target at the end of your turn the spell ends.

This technique was developed by the Archmages of Volitaris and may not have been developed in other lands. Check with your DM whether it exists in your world.