Target specific player to teleport mob to, for my hide and seek map

I'm trying to disguise players as mobs. I need to make sure the mob teleports to only the hider.

@p teleports to whoever is closer

@a and @r don't work either.

I have to give the player invisibility to disguise them and then tp the mob in a repeating command block with the command:

/tp @e[type=(mob)] (yourself or @p) 

This is a great use for scoreboard tags. You can give the player a tag and then use this tag to target that player. The command to add a tag would be:

scoreboard players tag <entity> add <tagName>

Change <entity> to the player name and <tagName> to whatever name you like.

Then your repeat command uses the specified tag in the target selector. I also recommend adding the count selector argument to prevent more then one mob from teleporting:

tp @e[type=TYPE,c=1] @a[tag=TAG]

Replace TYPE and TAG.

To remove the tag from the player:

scoreboard players tag <entity> remove <tagName>

Example commands using 'Hider' as the tag name:

/scoreboard players tag IronAnvil add Hider
tp @e[type=cow,c=1] @a[tag=Hider]
/scoreboard players tag IronAnvil remove Hider