he got turned into a GOD-TIER magic user after the Doctor Strange movie came out
Before, he was very much a low level magic user who's main skill was "fukking you over without magic", so him doing that plus low level magic... I don't have the words.John was on Doctor Who levels of fukkery.
SATAN satan said John was the most clever human ever born.
John scared GOD god into staying out of his business, by explaining to him that if he died, he'd go to hell.
And if he went to hell, he'd take it over in 400 years, tops.
Then God would have a Hell run by John to deal with as an enemy, and being "all knowing all seeing God" as far as John's lifewasn't worth that kind of hassle in the long run.
God agreed, and stopped watching John/influncing anything he was a part of.
But God was only trying to find a way to kill him because way back when John was dying of cancer, he tricked the three rulers of Hell into buying his soul at the same time. Since they couldn't all get it without going to war over it and giving Heaven the advantage, they made him Immortal. God was actively trying to find a way around it.
John Constantine = fukkery King
For real. Even Marvel was scared of a John Constantine character because of thr endless fukkery