System Shock

When failing a DC15 massive damage save, a conscious target will succumb to a System Shock. This is a reaction to the terrible pain the target has just received. This applies to both PCs and NPCs.

d10	Effect
1	The creature drops to 0 hit points.
2-3	The creature drops to 0 hit points but is stable.
4-5	The creature is stunned until the end of its next turn.
6-7	The creature can’t take reactions and has disadvantage on attack rolls and ability checks until the end of its next turn.
8-10	The creature can’t take reactions until the end of its next turn.