Stuck (plz help)

not gonna lie, this might just be my skill but… im stuck on level 3 of the second page of bounties. i always get through the first levels but i NEVER get past the boss! does anyone have any tips? its fine if not again, prob just my skill

Is this Mercenaries? Could use some more details

If you want, you can add me Jonius#11264 and I can have a look.