Minecraft – How to find a player with a score in 1.13.1

In order to increment by 1 anytime a player dies, the objective must be type deathCount. Something like this would work:

/scoreboard objectives add deaths deathCount Deaths

If you're making dummy objectives, you're using a similar command except with "dummy" in place of "deathCount." A dummy objective can only be changed with the following commands:

/scoreboard players add (player) (objective) (value)

/scoreboard players remove (player) (objective) (value), and

/scoreboard players set (player) (objective) (value)

You should run the following command before the /effect command, to make all entities with the tag "Detector" give all players within a radius of 10 a tooClose score of 1:

/execute @e[tag=Detector] ~ ~ ~ /scoreboard players set @a[r=10,rm=1] tooClose 1

And then reset the score after the /effect command has been run:

/scoreboard players set @a[score_tooClose_min=1] tooClose 0

You can replace r=10 with your detection radius, and tag=Detector with however you're identifying the mobs you are wanting to detect the player, or keep the tag and do something like to add the tag to mobs:

/scoreboard players tag @e[type=Zombie] add Detector