H4ND-EE

Because it wasn't obvious to me, this pet is found in the Underground part of Mechagon.

As of August 2020, this guy (H4ND-EE), Clanking Scrapsorter, and Lost Robogrip are the only 3 pets with the Omni Pummel ability. What's interesting about this ability is that it hits 4 times in one round (81 81 81 81) for a total of 324. Add Black Claw debuff and Shattered Defences and now the math really changes. (81 + 136) x 2 = 434. Now Pummel goes (434 434 434 434) = 1,736 damage!

Ever more against a beast pet.

It will be always of rare quality. It is one per instance. You can catch multiple if you will wait inside the instance for it to respawn (if you joined using LFG tool), takes around 1h for respawn.

There seems to be only 1 in the entire instance, as a front line pet; none as backline. And he always spawns in the exact same place. 

If you have cleared the instance, and someone has already captured him, just have everyone leave, reset the instance, and he will pop right back up. Rinse and repeat as needed.

Also note: You will see he has re-spawned on your mini map as you make your way back down to the vehicle transport after porting back in the final boss room.

This respawned about an hour after my friend caught it in the same dungeon instance.