Basically, going off by what I’ve seen in-game, they are an ultimate defense by hardening the bonds between atoms and molecules (and even go quantum level) against physical trauma, basically making sure his body doesn’t break apart when energy is exerted on him that should either damage him or kill him, probably, which would explain why he’s able to completely shrug off high-frequency blades (and snap one) and survive attacks that would be lethal to him. Although not making him invincible, it makes him incredibly resilient to most conventional AP and such types of physical durability negation, that’s why it’s “Pseudo-Invulnerability”, you need superior speed to bypass it (see what Sam and Raiden did)
He can also regenerate, be immune to diseases, radiation and poisons (idk why it isn’t added), manipulate and reflect kinetic energy and other energy sources, use magnetic powers and other shit, likely coming from the energy abilities. He is also able to channel fire by heating up his limbs, while also amplifying his striking strength as well, as he is shown performing feats such as busting magma pillars in extremely volcanic areas.
He can also react to speed amps.