Shares damage between all players. It doesn't share health/healing, only damage, so if you had poison and healing you could kill someone without dying.

Uses cloudwolf's Scoreboard Tree generator to make the /damage function work

If you wish for someone to not be included in the damage share, add the exempt tag to them (remove it to put them back in damage share):

/tag (name) add ds.exempt

/tag (name) remove ds.exempt