Cleansing Fire

Fire ignites burning only the intended target from inside out. The target makes a Constitution saving throw That target takes 8d6 fire or radiant damage, and takes 1d6 fire or radiant damage at the start of  each turn. At the end of each of their turns the target can reroll their CON save, ending the effects of this spell on success. 

When you cast this spell using a spell slot of 6th level or higher, the damage increases by 1d8 for each slot level above 5th. If cast at 7th level or higher  you roll a d20 and if you roll a nat 20 the target dies. when cast at 9th, and a targets health is 100 or less you auto crit this spell. A target cant be resurrected if killed by this spell.