Wild Mass Guessing for The Chosen Four.
Reginald Jr. is a Time Lord, and Ness's backpack is his TARDIS.
Well, he can certainly fit a ridiculous amount of things in there, including a workshop and a swimming pool. Jeff is a Technopath
If the other three have Psychic Powers, then why not Jeff? Given his affinity for gadgets, it makes a lot of sense. The true nature of Ness's PSI
At one point, Poo states that Ness's PSI is similar to that of Giygas. What if Poo's more on the nose than he thought? It's revealed on Moonside that Ness has some sort of link with Ninten's spirit. And Ninten is related through adoption to Giygas, since Giygas's adoptive mother, Maria, is Ninten's great-grandmother. Another thing to point out is the purple aura that Ness sports whenever his Berserk Button is pressed (in other words, when someone manages to harm Paula). As the Shout Out page points out, this aura is taken from Toby Fox's Halloween Hack, and is a representative of intense hatred. This would be unrelated unless you consider the one enemy in the hack who sports such an aura (namely, the Final Boss) has Giygas behind him. The conclusion is that Ness got his PSI from Giygas through Ninten.