Knowing there's someone watching his back means Sion can put all his attention into the battle at hand. He directs his Sneasel to attack, to feint, to dodge, drawing the Paras out and keeping it occupied while Ryner sneaks into range. Most of the attacks are relatively weak and would be inefficient if this were a normal battle, but that's fine. His goal isn't to just knock out the Paras, after all, but to allow Ryner a chance to harvest the mushrooms intact.

Which is to say, sure, they could just have Ryner's Growlithe take it out with super-effective fire attacks, but the request wasn't exactly asking for pre-toasted mushrooms. So, it's the slightly harder but hopefully significantly more rewarding method... And with over a decade of experience as a trainer himself and total faith in his companions to do their parts, Sion's pretty confident they can pull it off.