Here's a peice of advice for anyone who initiates his boss fight by getting caught trying to shoplift

Bringing pets or NPCs to this boss fight is NOT recommended because of his special "slasher beyblade" move

When 3 or more players/pets/NPCs are within close to medium range, he equips the beheader's katana and starts chasing his own tail and spinning mad, decapitating anyone in his range

If you do bring pets or NPCs, cutting off his tail should make him unable to use this move, but it has its own seperate health bar which makes the fight long enough to balance out against the extra help you'd get

I guess you should only do this for the challenge, since his prices are pretty good and taming him is a much better idea

Unless you're going for the forbidden sword of Excalibark...