explain what exactly you mean by 'merge his body into other objects', if you wouldn't mind. i can see that meaning a multitude of things, so i'd like to know which one of them is correct
Right! Sorry. I was trying to be concise.
Pseudo-scientifically, the gene mutability therapy was intended to make his genetic structure more adaptable, to unlock the shapeshifting process. This was unsuccessful, but it enabled his (he needs a name...Abel? Maybe Abel) cells to incorporate and mirror whatever material they come into direct contact with.
In practice, it's similar to being able to pass through solid objects, only unlike Kitty Pryde, he can't step through objects as though they aren't there--it takes pressure and time to smoosh his way in. Also unlike Kitty, he doesn't remain cohesive inside the object, but rather becomes part of it.
When merged into an object bigger than himself, he can spread his consciousness through it (to a degree--his range of extension is limited, but will grow with practice) and exert a limited degree of control over it proportional to the object's propensity for movement (that is, he couldn't make a granite cliff move, but he might be able to make some tree branches bend, and directing the flow of a stream would be easy).
He can also merge smaller objects into himself--this will cause the part of his body he merges it into to mirror the object's material.
She can also move through the darkness without hindrance.
By this, do you mean she can see in the dark without difficulty?