Reality Manipulation: The Beyonder has the power of Illusion Generation which enables it to warp reality at Class 3000 ability so much so that its illusions are indistinguishable from reality. With this power it may appear to use any power or talent to accomplish any task at Class 3000 rank. The range of this ability is roughly equal an entire solar system.
The Beyonder was discovered to be an incomplete cosmic cube. The ability to alter reality in a solar system, but nowhere near the level of universe or even galaxy destruction as originally represented (see original stats below). All those things like that the Beyonder did where illusion, a cube has vast illusion powers as well as reality manipulation and can appear far more powerful than it really is.
There ARE true Beyonders, they live in a formless white dimension and observe our own. Cosmic Cubes are used to store the energies from the Beyonders universe. The first race to create a Cosmic Cube where the Skrulls. They wanted a weapon that could turn thought into reality to battle the Kree. So Skrull scientists discovered a way to tap into the Beyonder's dimension and store a portion of the energies in that dimension in a cube, thus the first Cosmic Cube.
The ruler of the Skrull empire at that time used the cube for awhile to further his own goals. But after awhile the cube begain thinking for itself and would not do what its master wanted. Eventually it totally became indepentent and assumed a humanoid form. It took the form of its master, that Skrull ruler, and left for deep space, to explore the universe and imploy its powers. It descided it would use its vast reality and illusion powers to "shape worlds", however, because it modeled its body and personality from that Skrull ruler, it had no imagination and relied on the dreams and thoughts of others to give him inspiration. This being became known as the Shaper of Worlds.
That is the same kind of being that the Beyonder was discovered to REALLY be. The exstent of the "actual" reality warping a Cosmic Cube can do is about a solar system, its illusion powers can make it seem far more than that. So that is all the Beyoder really was. Still powerful, but nothing like it was thought to be. His destruction of a galaxy and certainly Death, where nothing but illusion.
It should also be noted that ALL the cosmic forces that presented themselves to the false Beyonder, (Tribunal, Eternity, Death etc..) where only dim shadows of there true cosmic all and in no way equal to their true power.