5Ds

Yugioh 5D's Spoilers!

In ep 19 of Pokemon Platinum: A Journey Brandon, WhataGeek, And Mah-Dry start joking about the 5Ds from Yugioh 5D's. They were confused about why there are 6 members of the 5Ds. This makes sense but if you go past the google search and into the fandom page you'll discover that there were 5 members til the last 12 eps where Leo, someone who wanted to become one the whole series but wasn't good enough at dueling, became one. Yjis would come up every now and again. And dueling, [], Whattageek explained this to them.

Who the 5D's are
The 5Ds are people who have a red mark on them that shaped like part of a dragon. Each one has a one of a kind Dragon-type Synchro Card that is super powerful.