1978’s Another Fine Myth is the first book in Robert Asprin’s twenty-one volume Myth Adventure series.
Skeeve jumped at the chance to become a sorcerer’s apprentice. The alternative was starving to death in the winter cold. But Garkin the mage proved demanding, insisting on practice, practice, practice. Moreover, Garkin wants Skeeve to stop using magic to steal.
Skeeve’s days of serving Garkin are close to an end. But they don’t end as one might expect.
Garkin is in the middle of a summoning when he is attacked! Garkin dies with an assassin’s bolt in his chest, but not before incinerating his killer. Skeeve survives intact, as does the demon Garkin had just summoned.
Garkin’s magical barrier around the demon died with the sorcerer. Luckily for Skeeve, demon isn’t exactly the right word for the visitor. This so-called demon is an inter-dimensional traveller. Aahz may look ferocious, but he has no interest at all in rending Skeeve limb from limb. He just wants to go home.
There’s just one problem. Garkin and Aahz were in the habit of playing jokes on each other during summonings. Garkin’s last jape was to strip Aahz of his magical power. Garkin is dead and there seems no way to reverse this. Aahz has a wealth of mystic knowledge in his head and no way to put it into action.
There’s another problem: the entity that sent the assassin. Isstvan, would-be conqueror of universes, is on the loose again. Step one: kill every magic user in one dimension and grab their magic. Step two: use that magic to overwhelm the mages of another dimension and grab their magic as well. Step three: profit!
It’s up to Aahz and Skeeve to stop Isstvan. While Aahz is temporarily out of commission as a magician, Skeeve still retains all of his magical skills. Unfortunately, his skills consist of minor levitation and light pyrokinesis….
As usual, I am showing the cover of the edition I actually own, which is the Dell MMPB. I suspect most readers encountered the Ace edition cover (by Velez1) 
or the SFBC omnibus cover (also Velez).
There may be a few lucky souls out there who own the Starblaze edition (by Freas).
These days I expect a that most readers will associate Phil Foglio’s art with the Myth books.
This book is a comedy of the zany variety, featuring many puns. Aahz, for example, is from the Perv dimension. He’s insistent that he is a Pervect and not a Pervert. Skeeve is from the Klah dimension, which makes him and the other inhabitants of his backward dimension Klahds. Of course, I myself eschew such a low form of humour, but I gather there are those who enjoy puns.
This is also a comedy that depends on many of the characters being idiots (most of the bad guys and sundry Klahds), naïve (Skeeve), or charmingly amoral (Aahz, the sultry and curvaceous Tanda). The title of the book recalls Laurel and Hardy, but the plot is closer to that of a Hope and Crosby Road movie.
In its day the series was popular enough to take over Asprin’s literary career. He wrote some fifty books, of which twenty-one are in the Myth series. When I was reading SF in the 1980s, most of the Asprin works I encountered were Myth books. Not great literature (IMHO), but they scratched a reader itch and thus made sure that the author could afford to live indoors, buy warm clothing, and eat. Huzzah for series novels!
Note that the preceding review may not capture the delirious enjoyment that Asprin fans doubtless feel when reading his work. My sense of humour, always slight, has declined to a shadow of its former self. This book didn’t work for me, but your mileage may vary.
1: I found a number of online images of the Ace Velez cover and most of them were fuzzy. I cannot imagine why this was so.