How can I change/fix this feature, that I'll see real enemy's hp? When I'm targeting myself, numbers are right, pet's also. It's like persentage, but in fraction. When it comes to mana (ally's and enemy's), everything is good.

You need to install an addon called "RealMobHealth". In Vanilla WoW, enemy health was hidden from the player.

Classic does not have exact health numbers. #nochanges