Ive been trying so hard and the only losses my team has is to him. Any advice?

I'm new hear too but i suggest you go to the troll caves get coins over time and buy potions.this worked for me make sure you have enough coins.

I took a look at your current pets, and I have some advice:

1: Una has a point she can use to upgrade her skills. I would recommend upgrading her Health

2: You want your first party pet to be a tank or health pet. This means either water, light, or shadow. Water is more of a tank and has a lot of support/shield abilities. Light will slightly heal itself and other party members. Normally this ends up just decreasing the damage being done to a pet but it can also heal if a pet is not hit on its turn. Shadow does more damage than light, but only heals itself. You can either spend gold to change what element Una or Sniper is attuned to, or I'd be happy to sell you this level 17 pet to you for 100g

3: In general it's good to have some revives in your inventory when fighting a more difficult boss. That said it's important to be able to tell when you can't win yet. If that's the case I would recommend leveling up your pets.

Hope this helps!

Thank you!