Mark Appel working on new pitch?

There's a quick note over at FanGraphs about a new pitch that Appel has been rumored to be working on this spring. I'm not a physics expert, but what they're talking about is something I've never heard of before.

“It’s insane,” said a source, who preferred to remain anonymous. “Once he’s got it down it’s going to be completely unhittable.”

Appel is said to have had tremendous success throwing his new pitch in practice and, according to the article, made Jose Altuve look ridiculous.