>>15450657Remove the head sticking out of Carbink, and compare what's left to the rock that Diancie stands/pokes out of. That structure is curiously similar, save for the color of the crystals. The closest analogue I can think of for two totally unrelated Pokemon would be Garchomp and Sharpedo's head stars and fins.
Come to think of it, a Mew/Mewtwo relationship (backstory clearly links them, but no actual connection beyond typing in the game's mechanics) is also a possibility, or at least my parenthetical approximation is.
At the absolute worst, it's easier to make a connection based on appearance alone between these two than it is to link Remoraid and Octillery.
I think Team Flare probably just shot lasers at a Carbink for a while (or some shit like that, there's probably lasers involved, this shit always has lasers) until it was mutated into the more beautiful Diancie.
(Also, weird head thing to dress-wearing humanoid happened before with Petilil to Lilligant.)