The Squiddy Shaw

Go to Pressure Pier and fight until a skirmish breaks out.  

You’ll have to keep trying this until Squiddy Shaw shows up as many times the wrong boss arrives.

@HeroGaming69To add to @spIash_damage‘s comment, he van show up before the actual boss comes along or while the boss comes so during the ‘kill remaining’ or after.

It’s a captain deadbeard with a squid on his head

The more you fight, the more likely you are to find him. I started 4-5 fights before he showed up.

I think I got lucky.

It only took my 3 skirmishes in Pressure Pier to get him to spawn, total, so it was actually my second when I actually started looking for him. Besides that he didn't even spawn as the leader/boss, he was just there spawned in like a champion while I was killing stuff.

I have tried this more than 30 times but he never appears

You can also find him around the boat when you start killing.enemies around there.