Playing some DnD, and I had players try to ambush some monsters at a higher level. Let’s build something that might help.
This options simulates taking massive damage to the point a creature is knocked unconscious. When a creature takes at least 50 percent of its maximum hit points in damage between the start of its turn to the start of its next turn, divine the amount of damage takes by its max hit point. Multiply that by 20 and round to the nearest whole number, rounded down. At the start of the its turn, the creature must make a flat d20 roll with a bonus equal to your Constitution bonus with the DC equal to the calculated value. On a failure, the creature fall unconscious As a bonus action, another creature can rouse the target back to conscious. Any additional damage also wakes the target up.