Meimi's magic tricks. According to Word Of God, she's better than her own father... And not only she can both do his old tricks besides her own, but she proved capable of performing one of his newer tricks after seeing part of it once (it was a substitution trick she used to make Rina believe that Saint Tail is a man in a drag).
This was awesome for Asuka Jr. too, for he managed to recognize the real Saint Tail in the middle of the copies.
The group of tuxedo-wearing dancing kangaroos from the prequel chapter is one of her strangest tricks... And one of the most impossible.
In episode 7, Asuka jr. actually succeeded in surprising and capturing Saint Tail. She only escaped because Rina, after being pranked by Saint Tail while in the surveillance room, attacked with tear gas without knowing she was already caught...
In the same episode, the director of the museum targeted by Saint Tail was complaining to Asuka sr. about Saint Tail successfully stealing a valuable archaeological treasure, and asked him how the police was going to take responsability.
Asuka sr.: "Ah... It's a nice painting. Don't tell me this is an imitation, too?"
Rina discovering that Meimi is Saint Tail in episode 8, and not letting herself be fooled by Meimi's attempts at disproving her findings (at least until Rina touched Saint Tail's moustache in episode 10).
In chapter 10, Saint Tail finally convinces Rina she's not Meimi. It's mostly a Crowning Moment of Funny due it involving faking being a man, but given how Rina had quickly saw through Seira faking being Meimi while Saint Tail appeared somewhere else in the previous chapter...
The anime version makes this even better by showing where the switching magic used to pull it off (by replacing Saint Tail with the male moustached substitute) came from: a couple days earlier, her father had shown Meimi part of that trick... And she reconstructed it.
That, and Genichiro's version: he switched himself with Eimi while holding Meimi's hand. Meimi didn't notice until she opened her eyes and saw she was now holding her mother's hand...
Saint Tail's apparition in episode 13 to steal Princess Rosa's Mirror: she appeared on a decorative chandelier while filling the room with the flowers named after the mirror's original owner, Princess Rosa.
In the anime-only episode 14, Saint Tail hacked in a video game console not connected to internet (that was also before internet use became widespread). She then stole a bicycle by making it fly in a Shout Out to E.T..
Episode 15 has the playful and non-indicatively named dog Little facing three jewel thieves. As soon as Saint Tail eliminated the gun from the fight, Little pulverized them.