Ashes to Ashes

All creatures in a 120ft cone must make a constitution saving throw on a failure they take 20d8 necrotic damage and have their speed reduced by 40ft until the end of their next turn, on a success they take 10d8 necrotic damage and have their speed reduced by 20ft until the end of their next turn. At the start of their next turn they must make a second constitution saving throw with dis-advantage if they failed the first one and advantage if they succeeded on the first one, on a failure they take 10d8 necrotic damage and have their speed reduced by 20ft until the start of their next turn, on a success they take 5d8 necrotic damage and their speed is reduced by 10ft until the start of their next turn.