Board Thread:Questions and Answers/@comment-5602817-20140709170000/@comment-25085317-20140715161129

I guess the arm effect is to show the changes of his muscles not to show growing muscles and they are just present in some of the OS transformations, just randomly.

For the vines part, its possibly just his skin transforming into those vines because all the transformations only transform Ben into aliens but not add any extra parts (off-course there are some exeptions like NRG, Echo Echo, Goop etc.), so lets just assume its also a result of the transformation which transformed Ben's skin into vines.