Ржавый робот-медвежонок

One v one?

I presume you're thinking Bite, Repair, Maul as a moveset?

The Anodized Robo Cub was in fact a valued member of my initial levelling team, so I'm fond of it, but I wouldn't consider it an especially dangerous PvP pet. If it had a Bleed in the first slot to proc the extra damage on Maul, maybe it would register.

Fer shoor, it is Tanky! 1709 or 1887 HP to start, and Repair restoring another 1K+, plus the Mechanical racial, it will take a lot of damage.

But it's VERY slow, and has no tricks, no avoidance, no weather.

I'm pretty sure any strong Elemental, especially with a heal. will give it problems. My first thought is P/P or H/P Autumnal Sproutling, would match it blow for blow and slug it out.. The P/S or P/B Shimmering Aquafly also occurred to me, with its type resistance to Beast damage, heal, and avoidance, though that would be a long and much less clear matchup.

Simplest just to use the book definition of a strong opponent - an Elemental that has strong type damage against Mechanicals.