I truly believe that a little comic relief is one of the key ingredients of fantasy, especially epic fantasy. And no, that's not the start of some joke, either.
Would the Lord Of The Rings movies have been as entertaining without a little comedic byplay between Gimli and Legolas? Could we have sat through three movies of The Hobbit without joking between the dwarves and Bombur's physical comedy? Would Game Of Thrones been such a massive hit without Tyrion Lannister's quips?
Epic fantasy requires darkness, but too much darkness can leave your reader depressed. You need a little light to both balance out the darkness and highlight it as well. Chapter after chapter of powerful, emotional writing will eventually leave the reader numb. Give them some light and shade and they appreciate the "serious" scenes even more.
Now I'm certainly not suggesting you need to go all Terry "Discworld" Pratchett and make it an out-and-out comedy. For starters, trying to be the next Terry Pratchett will get you only into one place - the reject pile or, if you're lucky, the bargain bin. Nor should you think you need to come up with lightning one-liners that would be worthy of some Ben Stiller comedy.
Instead, you need to focus on characters. Gimli and Legolas are the classic example. Individually they are serious characters but, put them together and add a little dwarf-elf rivalry and you have plenty of opportunity for comedic action.
As an example, two of my favourite shows as a teenager were Fawlty Towers and Blankety Blanks. The latter was a panel show with a group of comedians competing to come up with the best double entendre. Or, often, single entendre! Every episode was hilarious - but I couldn't repeat one of those jokes if my life depended on it. Fawlty Towers, on the other hand, had such rich characters that innocuous, silly quotes like "Don't mention the war" are enough to get people chuckling.
The key to being memorable wasn't the joke, it was the character.
So I love to create characters that offer that light relief. All of my books have them and in The Last Quarrel, this part is taken by Fallon's friends Gallagher, Devlin and Brendan and by Bridgit's father Padraig. Not only does it allow me to break up some of the darkness that the characters face but it also allows me to play with the readers.
For when you have a comedic character that, all of a sudden, is thrust into a life-or-death situation, the impact on the reader is that much greater. You expect the main characters to be put through the wringer. When the comedic characters are also thrust into the fire, it can create a powerful reaction. I want to make my readers feel a full range of emotions, so if I'm going to make them cry, of course I want to make them laugh as well. Ultimately I want the reader to be thoroughly entertained. And there's no better way than to give them a few laughs in with all the drama and excitement.