How do you get Clampearl's hidden ability (Rattled)?

Question

I'm a bit confused how to get it. No Pokemon that can breed with it can acquire it. So how can you?

Answer 1

Clamperl's hidden ability could only be obtained by getting it in the Sparkling Sea Dream World area from Generation V games. At this point in time, you would need to trade for one. Otherwise, there is no other way to obtain Rattled Clamperl.

Source

Answer 2

In ORAS, you can Dexnav chain Clamperls in order to get a HA one. Dive on one of the routes Clamperl is found.

Ability: This shows the ability of the Pokemon. When chaining there's a chance the Pokemon will have it's hidden ability (HA). When that happens you will see this next to the ability title. You will start getting the Hidden Ability when the Search Level is above 10.

Guide to Dexnav chaining and Source for quote

In USUM, on Route 15 (Which is one Ula'Ula island), you can SOS chain for a HA Clamperl.

Guide to SOS Chaining

Unfortunately, Clamperl is not in SwSh. It was not brought back in the IOA or the CT, either. So you cannot get a HA Clamperl in Gen 8 as this is written.