Ok so the Kingpin battle falls into 3 segments albeit they are all very similar.
First thing to note is how you harm Kingpin! What you need to do is charge up the sonic blast (hold
) and hit him with this. You now want to back off as he will get into a sumo pose and charge at you. Dodge him with
and a direction and he will hit the wall and become dazed. This is your chance to now attack him and do some damage. What I would recommend is standing near a wall as he charges you - this way you can just turn around and hit him without having to run to him.
The next two phases are the same to damage Kingpin - the only difference being enemies join the party. As Kingpin is quite slow, I recommend you take out the enemies first and then focus on Kingpin last.
Whilst the arena is quite tight, you will still be able to heal during the fight - just make sure you crowd everyone on one side, then jump to the other side of the arena and heal ASAP.