Book series about a magician's apprentice whose master is assassinated and has to be trained by another master, who can't use magic? [duplicate]

Question

I read this series in 1998 or something, so details are a little blurry. First book was about this apprentice summoning a demon, turned out to be his master's friend, but during the summoning, an assassin snuck in and murdered his master. The friend wasn't going to stick around, but then he found out he couldn't do magic anymore, so he had to train up the apprentice to get his magic back.

Other notable things: pet unicorn, there was a book about playing a champion sport to not get killed, fire breathing lizard friend. And there was a whole thing about becoming a court magician because they thought it was an easy job, but it turned out there was a major army coming to invade the kingdom.

Answer 1

Another Fine Myth by Robert Asprin, first book of the MythAdventures series.

Skeeve, a magician's apprentice and wannabe thief from the dimension Klah, tries to learn the basics of magic from Master Magician Garkin for several months but to no avail. Skeeve can do little more than float a feather or light a candle using magic. Wanting to convince Skeeve that being a thief is not as good as being a magician, Garkin summons a demon. During the summoning an assassin barges into the hut, and Garkin and the assassin kill each other. Skeeve is left alone with the demon. To Skeeve's surprise the demon politely introduces himself as Aahz. Aahz explains that demon is slang for Dimension Traveler. He further explains that there are thousands of dimensions with different races in them, and that he is from the dimension of Perv, making Aahz a Pervect, while Skeeve is a Klahd. Aahz is a master magician like Garkin but loses his magical powers during the summoning ritual (due to a practical joke played on him by Garkin) and becomes stranded in Klah. Aahz volunteers to take Skeeve on as his apprentice and teach him magic.