If you're building your first Commander deck, add in 8 - 10 depending on your Commander cost
It depends on what you are looking for
All of the new Tera Pokmon, such as Sylveon ex [Surging Sparks] have the opportunity to see success, and might be worthwhile pickups - same with Hydreigon ex [Surging Sparks] or even Tatsugiri ex [Surging Sparks]
events, new and casual players typically prefer using whichever deck suits their personal taste
She can attack with flying and vigilance and then use her mana ability to help bring in reinforcements that will receive +1/+1 counters equal to the number of other angels that you control
Design-wise, Fiend monsters usually appears either as classical demonic beings with menacing or otherworldly designs such as "Summoned Skull" or "Dark World" monsters, or strange creatures that would not fall under the Beast or Beast-Warrior types, such as "Sangan" or "Kuriboh"