Truly amazing! Its design is majestic, and its function quite creative. I just wonder how well it will function in the metagame without Gyarados as its partner.
One thing though, the method used for scaling its weight is flawed. This is due to the square cube law, which makes it so that when an object becomes larger, its mass (Which is interchangeable with weight) increases by a greater percentage. For example, a 2 meter cube that weighs 20 kilograms wouldn't weigh 40 kilograms if it was doubled in size. The 4 meter cube would actually weigh 8 times more then the 2 meter cube (Assuming it is made of the same material and has the same density), which is 160 kilograms.
If we account for the square cube law, Plasmanta, scaled up from a 2 meter, 70 kilogram Manta Ray, would actually weigh in at around 3000 kilograms! That's over 50% heavier then Primal Groudon!
That said, I don't have a problem with the current weight. The vast majority of pokemon have weights that are disproportional to their dimensions and/or anatomy (I'm looking at you, every pokemon that's bigger then a human being ever). So, I don't really mind anymore. Its just that the science nerd inside of me felt the need to point out about the scaling error.
And again, I have to say it looks amazing, and I look forward to using it in the CAP metagame.