Try taking a look at the wiki: https://thelastsovereign.miraheze.org/wiki/Incubus_Prison.
I also wrote a walkthrough for 0.58.1 you can find here if you want a second thing to check: https://thelastsovereign.flarum.cloud/d/78-the-incubus-prison-0580/35
Here is what I wrote about that section:
Equipment: Wynn's Scepter, Offensive Rod, Frozen Hat, Heretic's Robes, Ribbon de Iris
Enter Tynaburg > Spike Tent. Follow the path north for a shiny (Mana Leaves), healing as appropriate (do not over heal). Leave to heal and reenter the Spike Tent. Follow the path further north for a shiny (Sarai - Scroll of Sarai - Consumable). Use the Scroll of Sarai. I had 165 MP at this point. Heal when you have 15 MP left. Leave Tynaburg. Enter Castle Vera. Fight the light blue flame in the northeast corner.
Note: This section starts after fight 99.
You can also join us on Discord and get help in real time if you're interested.: https://discord.gg/jKMncKyTZ7.