From the Sky Key, he exist in another dimension where only transcendental matter or laws can affect him. Then from the Saint key he resist to time abilities and from Deity Key he has the Mirage World blocking time and law powers which is a 5D ability.
Mirage World is a Dao, a rule that transcend countless spacetimes and all ordinary laws of the universe; its like a tower with multiple floors, all the laws and beings of the universe are in the first floor making impossible to interact with the Dao that exist in the second floor but reverse is possible. Mirage World is a paralel world of the reality that appeared once Xue comprehend its true meaning. Its the source of all illusions, all phantasms, all any kind of such powers and so it grants him illusion, dream, sleep, mirage, perception, soul, pocket reality manipulation, can make it substitute the real world making him be omnipresent across it. He's also will not die as long as it exist so basically type 8 immortality on a 5D ability. It also makes him able to become an illusion that can't be affected by the laws of the world, to manipulate the void, control the physics of the reality, plus granting him alk kind of resistences.
He has 3 true him - as long as one exist, it will be able to create the others. One is in another Cosmos and one in the hidden space where the laws exist which even Rulers (Dao users -5D hax can not reach easily). The Mirage World before it even become a Dao was equal already to the True Meaning of Extreme Piercing which can pierce though countless dimensions. Rimuru can't interact with 5D structures so he can't do anything to this.
He can fight from wherever he wishes as long as its in his range. In the verse, each Cosmos has different Supreme Laws that exceed the Rulers which is why Xue has another him in another universe to have a failsafe in case his day by day him dies. Then the third him stays in the hidden space to comprehend more laws but all can do the same time things.
Sealing won't work as he not only resist but the Mirage World protects him.
Doesn't make a difference if the speed is equalised as Rimuru can't put him down at all while he has multiple ways with just the Mirage World, then he has 2 more Dao (Slaughter and Ripple) so other 5D powers with multiple abilities. He also has the Black Gourd.
Also his 3-A is the True God key not World Deity which is 3-B. All these things mentioned are up to just World Deity while the key for 3A has even more hax: such as controlling others through their avatars, clones, and the like as long as they share memories with Mirage World. Can create any laws he wish. Plus he has the Voidification ability making him a part of the Higher Dimension increasing just his defense to Low 1-C basically he can be a 3-A Ap with Low 1-C durability being.
Its a pure stomp.
