regarding the thing's ability to change back and forth from the thing to ben grimm;
Ben Grimm originally had the power to transform back and forth into the Thing at will, and in the first few months of his career he frequently did so by subconsciously triggering the change. After meeting Alicia Masters, and finding her so enamored with the Thing and NOT Ben Grimm (as he briefly became in her presence), Ben set up a series of psychic blocks which prevented him from transforming or being transformed back into Ben Grimm permanently. On a conscious level, Thing was completely unaware of having done this and continued asking Reed to find ways to change him back to normal, but even the successful attempts never lasted very long. During one period he reverted to Ben Grimm after prolonged exposure to the Hulk's gamma radiation, and Reed outfitted him with an exoskeleton to boost his strength, which was externally identical to his Thing-hide. After being blasted with cosmic rays by Galactus, however, Ben transformed back into the real Thing, stronger than ever before. Another boost in strength came after a Skrull aging ray brought him to the point of death, only to be reversed and his body revitalized by the process.At one point, Reed had created what he thought was the ultimate way to turn Ben back to normal -- a process which not only would revert him back to human, but place a "cosmic lock" on his metabolism which would prevent any further change in his body from occurring after the procedure ended. Unfortunately, Ben's psychic blocks remained in place, and he was only reverted back to the lumpy oatmeal look, seemingly forever. Only after Franklin Richards accidentally used his vast powers to age himself to adulthood was Thing reverted to his "un-locked" rocky form and Reed made aware of Ben's psychic blocks. As time passed, Ben and Alicia began to grow apart from one another, and the blocks began to weaken. Once they were separated by vast physical distance as well as emotional distance, during the Secret Wars, Ben began to revert back to his human self, first by chance, and later through an act of will. Wrongly believing Battleworld's unique environment to be responsible for his transformation ability, Thing stayed behind after the Secret Wars to contemplate his life. Unfortunately, a series of events on Battleworld led to Ben's human side gaining sentience as an independent being and becoming corrupt, and when this manifestation was ultimately slain, it removed Thing's transformation power, "forever". Returning to Earth, Ben rejoined the FF and was later caught in another cosmic storm while on a space mission, transforming into a larger, more powerful version of himself with pointed stalactite rocks in place of his smoother ones, and a strength level which exceeded Class 100 significantly.
When Reed designed a special device to drain off additional magically-enhanced cosmic energy from Johnny, the Frightful Four broke in and in the melee, Ben was knocked into the device, reverting back to his human state for the time being. He still accompanied the FF on missions, using a special attaché case that opened into tesseract space to store more matter than physically possible. He kept a rocket-blasting pistol and his old Thing exoskeleton in there. Due to personal problems developing between him and his girlfriend Sharon Ventura, a She-Thing at the time, Ben willingly subjected himself to cosmic rays to become the Thing again. Shortly before Onslaught, he discovered a metamorphic ray machine that allowed him to transform back and forth whenever exposed to its beams, but the device was cannibalized for parts in battle with Onslaught. Sometime after the Heroes Returned, Ben was exposed to the alchemical potions of Diablo and the transmutating stone touch of the Grey Gargoyle in short order. These two unique occurrences gave him the power to transform at will by making him Thing-skin akin to an organic exoskeleton which he could summon on and off his body on command from extra-dimensional space. This eventually proved problematic, though, when Ben began spawning psychotic Things from his exo-skin. The only way for Reed to stop the "Ever-Lovin' Blue-Eyed End of the World" involved permanently making Ben the Thing again.
this was taken from monolith's power descriptions archives on uncannyxmen.net