So Im on the battle in Fugus Grove with that guy.. Cereon and his minions I believe. Ive been fighting with Sylesti that are level 16 and 17, but even though theyre level 15 they beat me every time. What should I do? I wondered if maybe their elemental attunement was the issue? Should I train up some other Sylesti? Or should I just take these guys someplace else and try to level them up more? (Although thatd be a Slow process yikes)

Thoughts? Id really like to progress but I cant even do normal battles in that area because I arrived at the boss battle!

Looking at your current party pets:

Marinus
Lv17
water
1 str/int
Equips:
Relic: Newbie's Mundane (Uncommon, lv0, no orientation)
Armor: -
Accessory: -
Accessory: -

Un-named
Lv16
Air
1 HP
Equips:
Relic: -
Armor: -
Accessory: -
Accessory: -

The issues immediately leap out at us.

Water is more oriented toward being put in the lead slot for doing Tanking, and should be stated toward HP or Agi at first, and equipped for Agi and Str (Assassin gear.)

Air is a Glass Cannon element, and should be statted and equipped for Strength and Dexterity (Myrmidon gear.)

Equipment is really important- not having any cripples your damage output and defences.

A single unoriented uncommon level 0 equip isn't really going to cut it in terms of helping either.
You'll want to get both higher rarity and higher level (at the moment, lv10-15 equips is the highest level you can give these pets. Rare rarity, but epic if possible is likely the best you can do in terms of rarity (I don't think there're legendary equips under lv20, and mythical are only lv25 and lv50)

You can get more equipment via fighting, buying from the broker, or by doing missions (there's a guide to missions in the Player Guides forum- missions also give things like gold and healing items)

Ah, thanks so much for your help! I admit I just equipped that relic in the tutorial and kind of... forgot about equipment and such afterwards. Ill pay closer attention to it in the future ^^ thanks again!

Also, leveling up your Sylesties will help a lot. Try for 19-20, I was able to do it easily at 20.

I beat them pretty handily after some restatting and equipping! Thanks for the tips, you guys!