Conservation of mass? What conservation of mass?
In the world of implausible super powers, the ability to instantaneously morph from a single cell organism to a giant dinosaur (or from a small boy to a 100 foot tall alien) certainly requires a greater than usual suspension of disbelief.
The boys and I have discussed just where is it that Beast Boy and Ben get (or store) all that extra stuff? A personal pocket dimension is the leading explanation, although it is pretty clear that the kids don't really get the concept of mass.... I probably don't either, really.
I got started on this one long after the time I should have already been in bed, so it, as Ansel would say, "is not some of my best work." It's not clear what is going on in back with the Tyrannosaur and Ben's alien Way Big. The intention was that the alien was holding the dinosaur... or at least patting him congenially on the back, but it's not really working either way.
And the placement of the two guys in front is unfortunate and sloppy. Revisions are just not possible on napkins...although I did move Garfield and Ben's arms around a bit so that it looked a bit less like they are reaching for one another's groin. There is a very active subgenre of fan images of that sort of thing, and I was definitely not aiming to be part of it. Nonetheless, their postures and expressions, still seem a bit peculiar.