A group of Gray Dwarves, nothing more. Even if they have Spiritual Energy, it's not a big deal. Adding in the Shifting Beast doesn't change much—reality isn't the same as games. In games, even a commoner can damage an Ancient Red Dragon with a good dice roll. In reality, that's impossible. Leon was confident Cecilia could handle them easily.
If one intends to learn Spiritual Energy, then mere observation won't suffice. Reading ten thousand books pales in comparison to walking ten thousand miles. There's no better way to gain firsthand experience than by battling enemies who wield Spiritual Energy.
As for Mind Flayers, who are also proficient in Spiritual Energy—perhaps letting them serve as Cecilia's opponents would be more ideal—Mind Flayers are powerful aberrations. Even though Cecilia is a Green Dragon, a young Green Dragon would struggle to deal with that many Mind Flayers. A single moment of carelessness could spell disaster. It's simply not suitable to use them as opponents.
