The Collector - Boss monster (Patreon)

The salesman finishes his collection, looking at you all expectantly. In the end, you decide not to make a purchase. The salesman seems fine about it till he notices a golden pin on your party member's chest. He points...

"That pin you have there. Sell it to me..."

The party member replies, "no... it's been in my family for generations". The air around the party begins to grow colder. 

"GIVE IT TO ME" the seller screams, as suddenly his form bulges and distorts. One hugely muscled arm smashes into one party member, sending them flying. Another arm slashes out with acidic claws, cutting through the armour of another. Still more and more arms appear, blind siding your team with everything from spells, weapons and curses. 

Your party all incapacitated by a blizzard of attacks. The monster reaches out, gripping the head of  the party member with the pin, raising her up. 

I could always do with a spare... in slow motion, the collector tares her arm and shoulder away. Claiming the arm and the pin. Before disappearing in a flash of magic.

DM notes - got players that keep messing up, humble travelling sellers? Drop this guy in front of them. Guaranteed they won't do it again.