With how it's going, the boss is gonna be 4 adamantium golems.
And it takes controls of allied golems, explaining how the previous group got destroyed so easily.
She's technically a hero, and Sera is the daughter of a demon lord. I guess the demon lord would have some way to equalize the fight. It'd be pretty boring otherwise.
Antagonists coming out of nowhere and ruining the day without a decent explanation for it is lame. It's fine if they laid out a carefully planned ambush or their power is stealth, but it doesn't look like it, in this case.
I'll try to guess what the riddle is: You have to inscribe what a statue with the 4 combined traits would look like. So, wings, horn, claws and sharp teeth.