A tucked gainer off the end is a B, and a piked gainer is a C. I've never seen someone do it off of two feet, but according to the 08-09 update, any backwards salto that starts facing out is considered a gainer.
I saw somewhere else that it was a C, and didn't believe it myself so wanted to check here. I can't even do a roundoff layout, let alone a layout double twist dismount, which is a C also, but can do a tuck gainer into pit; will try to take it to the beam and also work on piking it!
The pike is only a C if the gainer is off the end of the beam, with your head close to the end of the beam. Off the side of the beam, its an A.
This dismount off the end is not easy, it takes a lot of time to develop for safety reasons! Lots of work tossing the gainer straight out, landing on the back on a big resi mat, then adding the height to add the flip much later.
My thoughts: if you arent at the skill level to do a round off on the beam, you are not at the skill level to do this dismount safely.
I can do a roundoff on the beam, just am not a great twister. I realize it's dangerous if not done correctly, thanks for the heads up. I have a beam into pit setup I can do when I am ready; for now I will keep working gainer off the edge of the floor, and also the drill you mentioned onto a mat stack. I am level 8 not 9 anyway, so a B level dismount (tuck) will work for me.