I have been trying to defeat king desius for a while. My current pet team is all hallows eve, level up and ivy's glow. Any advice on how to get past this area and what I need to do would be much appreciated!

its ok im stuck too

Try going back and making sure you got all the seals? That was a big issue for me. I actually never got any of the seals so I just had to use brute strength.

Potions, use those to heal your pets
you need a strong team power through him to
only attack him, don't go for the ones next to him
(they are ifinit)

Use pets with wind, earth, or dark. Fire is for multiple opponents, and thus their attacks will be weaker if directed at a single opponent. I also used lvl 59 pets. just to be safe. Also, equip a few revival draughts and use high level armour. Armour, accessories, and relics make a whole lot of differents. Also, proficiency points should correlate to their elements. You want a lot of strength for tanking pets, and a lot of health for weaker pets with low health, etc.

Thank you to everyone who offered advice on this. I have passed that part and am currently exploring the lost grove now.