Note: For a game to be on this list, the tone of the game must be mostly serious - otherwise it doesn't qualify as relief.
If the story begins to get too bogged down in the murky depths of evil and darkness, the comic relief comes to cast a ray of refreshing light on the situation. Generally, these characters don't follow the protagonist everywhere or, if they do, they only behave in a silly or witty manner between story development sections or very large fight sequences for the purpose of breaking them up. Games without comic relief tend to burn the player out on the experience by constant exposure to serious content. The humor the comic relief uses depends on the setting to an extent. If the setting is bleak or brooding (such as in Half-Life 2), comedy tends to be in the realm of witty dialogue and satire. If the setting is cleaner or more fantasy-oriented (MGS4), the comedy tends to lean towards slapstick.