Welcome and enjoy what is one of, if not the most unbeatable guy in the herald tier.
To put it into perspective -- all that you see here, was done in 1 year of existence/publishing history, most of which was him just getting used to his powers.
Let's begin.
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“Perhaps this is the ultimate freedom. The freedom to leave.”
He is immune to physical attacks, as demonstrated here against Wonder Woman's attacks which he handily phases through, absorbs and redirects the kinetic energy back to her:
And though his 'strength' is energy based, Asmodel [a trans-dimensional angel who was beating the piss out of J'onn just before this] doesn't have much success trying to overpower him:
Blue Superman encounters a guy whose power is to psionically get every power. He wants to imagine a weapon, to be invulnerable, to be stronger than his opponent? He just thinks it, and it is.
Solution? Blue S takes control of his psychic energy, transmutates it and disperses it, depowering him.