Before time began, there was the Cube. We know not where it comes from, only that it holds the power to create worlds and fill them with life. That was how our race was born. For a time, we lived in harmony, but like all great power, some wanted it for good, others for evil. And so began the war - a war that ravaged our planet until it was consumed by death, and the Cube was lost to the far reaches of space. We scattered across the galaxy, hoping to find it and rebuild our home, searching every star, every world. And just when all hope seemed lost, message of a new discovery drew us to an unknown planet called... EQUESTRIA.

But we were already too late...

In terms of MLP continuity, the story takes place before, during, and after the events in the episode, The Lost Treasure of Griffonstone.

In terms of Transformers continuity, even though it is unrelated to any of the universes, it does borrow elements from several timelines (most importantly, the Aligned continuity).

Also, both MLP and Transformers are owned by Hasbro.