This one is a little tricky and it relies a little bit on luck:
1- Keep attacking the boss and use skills on CD. You will do Dagger, Vitamin, sticker first, then dagger vitamin next, repeat on CD.
2- Every shot of yours will have a chance to spam a chicken. You need chickens to tank the boss. If you are unlucky with chicken spawn you are cooked lol
3- Move around the boss in circles so you dodge all of his skills ( when he throws punches just step back and keep shoooting ).
4- IMPORTANT, when he spins, don't run away, charge through him and keep attacking, you will heal yourself up quickly thanks to the healling ring