RileyXY1
Young Battle Trainer
I agree. We JUST had Nebby as Ash's surrogate Pokemon and I can't imagine they'd immediately repeat the plot with Poipole. It's clearly gonna play a big role, and it's it's the perfect choice of UB for Ash if they wanna give him one. The only other scenario I could really see would be the Ultra Recon Squad showing up and capturing it.
Just because Naganadel is technically considered a legendary by the games doesn't mean it has to be uber powerful. Even by the games standard it's BST is only 540.
Also, Gladion's had a legendary almost since he debuted.
Naganadel is currently in Ubers. It's really good and can sweep entire teams thanks to Beast Boost.