Steph,
the main reason ive had it with my masters and think it is one, is because of that one on Alans page, in hand it looks Mastery, and the seams do to but the base ? i dunno i could be wrong, i just didn't really know where else to stick it lol the batch that it came in did not have one single new mib in it so i know it's not new, and this isn't one of those "are you sure one didn't sneak in" cuz im positive !
Alans description: Some Sunburst-like marbles with a colored transparent base have been identified as Master marbles. One type that has been called "Crab Claws" has a transparent green base and yellow filaments and strands. These appear to be rather scarce.
Heres the pic he posted..
It's hard to get inside the matrix of mine, but there are yellow strands that are spread out sunburst like...