My advice is to utilize Hel, bring 2 kind of mana potions (preferably mana potion and super mana potion) to make her fire each time the mana block expired (every 3 turns). Don’t let any opposing hero gain mana. Do not bring axes, arrows, bombs, or dragon. Bring 2 healing potions and 2 mana potions instead.
For the orher 4 heroes, you can bring Kiril, Caedmon, & Li Xiu. Don’t you have any other maxed blue heroes??? Do you have any other healer? If no then bring Sabina (you might need to level her quickly before the event end).
Utilizing that strategy with Proteus (I don’t have Hel) allow me to complete legendary wonderland with 2900 TP back in February.
My legendary team was Kiril, Grimm, Frida 3/70, Kunchen 4/50 and Proteus. I had no problems with the bosses but the mobs took a bit to kill. The combo of attack buff + def down + elemental def down is awesome, it can kill any monster. Having 2 healers helped the team, a lot. Most of the credit goes to Proteus tho. He shut down the bosses and all he asked for was small mana pots. He’s the real MVP.