WPvP has alot of dirty world buffs n consumables, if he phases out of fights i´d say with 90% certainty that he abused overpowered consumables n dirty wPvP tricks aswell.
Outside of scripting theres not really any straight up cheats in the game. There has been countless exploits like WW monks touch of death oneshotting people, frost dk stacking dmg on low lvl mobs n oneshotting an entire raid, rogues hitting low lvl mobs n oneshotting people with shared damage etc.
Healing on low level mobs with leech has existed for ages aswell. Even 1% leech will heal you like 30m hp if you hit a mob for 300000000000000m damage with an instant cast or hell even a random aoe.
Without more information its impossible to say what he was abusing but anyone who bothers to use follower dungeon to phase out of PvP is 100% the kind of person who also exploits all consumables at his disposal.
uhm, i feel called out
but im sure it wasn’t me, because i haven’t been figthing anyone for a week
but there is different ways he couldve done it
if u mean he was disappearing and coming back, it might just be entering any sort of instanced content
if you mean he couldn’t have been target there is a few items that can do that