Scholar Mode could work as a Xros of Mysto and Knowledge (or is it Genius?).

What would make Treasure Mode different from Captain X Beard is that he is capable of controlling anything that is considered valuable and not just limited to literal treasure and money. Treasure Mode controls the very concept of value while Garbage Mode controls the concept of dereliction and worthlessness. He is essentially a living treasure hoard himself also, much like how Garbage Mode is a living junkyard, he can absorb and assimilate anything considered valuable into himself to boost his power and eventually transform into his Colossal form but he CANNOT outright create treasure from his body like Captain X can, this goes the same for Garbage Mode and junk/garbage/neglected things.

But with all that said, he could still work as a Plus Mode as Captain X regardless, this was just the general idea for Treasure Mode and Garbage Mode to be counterparts themed around the concepts of value and uselessness.