Was Crocodile stronger at Marineford? Or was he holding back in Alabasta?

 During the Alabasta arc, Crocodile displayed a level of power that was initially considered overwhelming by the Straw Hat Pirates. He possessed the Logia-type Devil Fruit called the Suna Suna no Mi (Sand-Sand Fruit), which granted him the ability to control and transform into sand. He had a reputation as a Shichibukai and controlled the desert kingdom of Alabasta from the shadows. His strength was showcased through his battles with Luffy and others. At Marineford, Crocodile was present as part of the war that took place at Marine Headquarters. While he did participate in the battle, he didn't display the same level of dominance as some other powerful characters present. This has led fans to speculate that he might not have been as strong as initially portrayed in Alabasta. It's important to note that power scaling and character abilities can be subject to interpretation and development by the author. Oda often keeps details deliberately open-ended to keep the story intriguing.

What makes our dimension or universe unique from all others?

 Our dimension, or universe, is unique in many ways, but one of the most fundamental differences is that it is the only universe that we know of that contains life. As far as we know, our universe is the only one that contains the conditions necessary for the formation of galaxies, stars, planets, and life as we know it.

Additionally, our universe is unique in its physical properties and the fundamental laws that govern it. For example, the physical constants, such as the speed of light and the gravitational constant, are thought to be fine-tuned to allow for the formation of complex structures like galaxies, stars, and planets. Similarly, the fundamental laws of physics, such as the laws of motion and thermodynamics, are thought to be necessary for the evolution of life.

Overall, while it is possible that there may be other universes out there, the one that we inhabit is unique in many ways, including the fact that it is the only known universe that contains life and the fundamental laws and physical constants that make that life possible.