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A puppet is nothing without its master, and we've already seen an entire town under the effects of the mochi, which ended up as a complete nothingburger. Pecha may be a sniveling little shit desperate for love, but he's ultimately not malicious (and his planning skills are non-existent), so I'd bet he'd just make Terapagos do the mochi dance or something equally ridiculous yet harmless until he either grows bored or bonked senseless by the trainer and/or Ogerpon.
Then again we've seen Terapagos break off from a binding device and go berserk as a result, and with the mochi's enhancing qualities at play, it might be a tough raid to solo.