MEGA's aura has ways around that. If he consciously strengthens its effect, he can nullify all forms of magical/supernatural ability and paralyze the mind, preventing skills and traits from being used. It also helps that the High 1-A soul/minds he affected also possessed innate resistances to things like madness, illusions, and etc at the level - yet MEGA's aura can bypass such things.
Well even if Joshua does lose his mind, he does not need it to fight, he's fought hordes of Evil Gods with varying abilities for millennia without one. Plus his [Steel Armor Kokyu-ho] gives him resistance to effects like Fatiuge, Paralyzation, Slowness, etc.
Other pseudo-active aura traits include instant death via bloodlust/killing intent and omnidirectional spiritual shockwaves that can resonate within one's mind, body, and soul until they are destroyed.
Stuff like instant death attacks can't normally penetrate Joshua's defensive aura, which has passive reality warping. And since he has mastered every Multiversal Force, he is able to use spiritual power, which can clash and repel other spiritual forces.
The issue would be getting hit by MEGA's attack at all, since that would reduce him to particles.
Being reduced to particles isn't an issue for him, he's made up of the 'Steel' which is the foundation of everything, including matter.
Also, MEGA's "Lightning God Zeus" technique can just instantly obliterate all of his built-up resistance layers simultaneously and hit him anyways. It able to do so against a that being that was using her "narrative evolution" powers to siphon information from his abilities and manifest/evolve countless layers of resistance based on that. That could potentially be a one-hit kill, as MEGA is able to negate an absurdly high level of High-Godly Regeneration with his moveset.
His mastery if Steel Strength allows him to manipulate things like life and death, so dying is hardly an issue. And on the off chance that he does die, his [Stealth Mastery] allows him to enter a state of false death where he heals rapidly before his true death.
MEGA once reached "perfection" which was the amalgamation of every single thing he could possibly do right across every possibility, and then ditched that technique because he got obliterated by high-tier Cultivation people effortlessly and decided it was ass. He went on to make substantially better techniques which are effectively more perfect than perfect.
Joshua's perfection is focused on the 'present' cut off from the past or future. It's not a matter of relying on other possibilities, there is simply no possibility that can do better than he can, and even then he continued to improve to the point all other possibilities involving him disappeared at the speed of thought.
And if it comes down to it MEGA can tap into the Imaginary Axis, which just manifests his imagination as an attack. It is a technique that is "unpredictable, unintelligible, and unknowable." Regarded as the pinnacle of martial arts, inaccessible even to people who can do all that probability stuff I mentioned before.
Legendary-tier beings are able to invoke reality in order to see the true nature behind everything. Because of this, they have no battles where they have zero inklings and can see through any attack, to the point that 'unknown' attacks don't exist. It doesn't matter how atypical, or meticulous.
In fact what you described is what they call spiritual power, which is defined as unreasonable, contrary to common sense, and absurd. It's a power that can turn belief and imagination into reality. Of course, it can also just be used to manifest a concept of unreality.
Funnily enough, MEGA has specifically changed the concept of direction before, in the same Void world that I mentioned earlier. He was able to manifest all directions in order to move spatially after direction was voided as a concept. So he could just change the directions back to normal.
Damn, the drill didn't work out of verse, or in verse ;-;