Kingler

Well it has really high IVs with is its best defensive moveset, for whatever that is worth. Kingler's max CP at level 30 is only 2300, at level 40 is just shy of 2700. But what else are you ever going to use Krabby candy for?

Kingler has really high base attack and defense, but low base stamina and no strong offensive charge move.

Unfortunately with the low stamina, it is probably not going to get quite the same kind of crazy chaining of defensive Water Pulses the way that Vaporeon can. By the end of a fight, a defensive Vaporeon has gained a lot of extra energy from losing HP. (Each pokemon gains 1 energy for every 2 HP that it loses. Gym defenders have doubled HP.)

Using only metal claw on Kingler is actually the strongest steel type attack ever. Use it to defeat Lapras, which is weak to steel type. And for most case, don't power it up, a Lv 30 Kingler is already very good.

You may find this chat useful.
It seems relevant.

https://pokemongo.gamepress.gg/q-a/give-kingler-try