We see Sebek’s unique magic for the first time in Book 7, which he says he discovered when striving to ensure that he would be able to go running faster than anyone else if an emergency arose for Malleus.
Sebek explains, “It turns the caster into a bolt of lightning that can be used for maneuvers or offense…But it remains so unrefined that it leaves me with harmful aftereffects when I use it.”
As the spell grants him highly increased speed Sebek says that he could use it to catch up to Lilia and Baul (the group had become separated), but he would be dead weight afterwards due to the after effects.
Sebek says that he hadn’t planned on using it in front of others at all until he had completely mastered it.
He uses it a second time in Lilia’s dream to save Silver and Lilia from Silver Owls.
During Lilia’s dream we learn that Sebek is possibly bilingual: though we never see him speak the same language as the guardsmen (“an older fae dialect”) he says that, while not fully versed, he has a general grasp of their language.
Sebek explains that speakers of Briarland’s native language have become somewhat rare, but he learned some from his mother and grandfather when he was young.
Due to the narrow hearing range that humans have people like Silver and his own father cannot make linguistic sense of it, but as Sebek is half-fae he can detect minute sounds that are inaudible to humans.
Twisted Wonderland Reference Note 