COUSIN FETHRY
Here's a stocking-capped duck who's perpendicular to the world.
Full of incredible enthusiasm, Fethry's out to bring big ideas to fruition and to achieve something great, be it as a skiier, animal trainer, schoolteacher, or even marriage counselor. He's always got a new job or a new craze from which he hopes to find personal success - and more importantly, to uplift the world at large, by sharing the thrill he's after with any and all who are near. He seems to have what it takes for the task: a creative mind, a never-say-die attitude, a wily grip of logic, and an intense love for his fellow man.
Pair all of these with an innocent, but total inability to see what's going on around him, though, and you get Fethry as he really is: a pesky neo-beatnik who always has others in frustrating spots - or himself in breathtaking muddles that he rarely sees as his own fault.
Fethry has brains, but by not seeing when he's misunderstood a situation, he'll imaginatively do what's not required. Fethry has a helpful attitude, but his blind-sightedness causes him to ignore how his "help" causes chaos (and should its recipient protest, then they're obviously too ignorant to perceive the greater good that Fethry is trying to achieve). Fethry believes in the empowerment maxim that "if at first you don't succeed, try, try again," but he takes it too far; so that the experience of doing things is the important part, and success is, comparatively, unimportant. Even if he meets defeat, he usually just marches on to his next venture, taking a lesson from nothing.
There is one thing Fethry is legitimately good at: mind games. He's quite good at talking others into going along with him - or else leaving them so boxed-in with his arguments that they can't respond clearly, which for him is as good as consent. In fact, he'll even trick or guilt-trip others into providing help or compliance, and do it successfully. He assumes that when his noble goal is accomplished, the people he tricked will be glad they assisted him. In reality, they almost never are, but in his own mind, all is well.
Yet even here there are exceptions. At times, Fethry is both made aware of his failure and held accountable to it; and in such cases, he can do nothing but try to talk himself out of the blame. This is when his arguing skills don't work - that is to say, not the same way. He usually keeps himself free of the blame. But he also gets it pinned on somebody else, and his efforts to get the other guy out of trouble invariably make said other guy's situation only worse.
Fethry delights in the world as a whole, but boasts a special love for nature, art, and animals, which is unreciprocated. He also loves his friends and relatives, which means that they're his most frequent victims. They may try to go along with him, attempting to convince themselves that he can't be all bad. They may think Fethry will cause trouble, but that they'll merely have fun watching from a distance. Wrong. Fethry is a disastrous sorcerer's apprentice to Gyro, a walking disaster in Scrooge's businesses (where he's part-time reporter for the miser's Duckburg Chronicle), and a charming underdog whom Daisy and Grandma at times defend - but are often sorry for having defended.
FETHRY AND DONALD
From Fethry's side...
Fethry is (and somewhat without explanation) dearly, inordinately fond of his cousin. It thus follows that Fethry should want to give Donald a more satisfying existence. Time and again, Fethry invariably misinterprets his own latest craze as "the spark that kindles the fire" - The One Thing That Will Immeasurably Improve Donald's Life - and pushes it on Donald with a flabbergasting eagerness. Fethry might even trick Donald into going along with whatever Fethry's pushing today, the idea being that in the end it's for Donald's own betterment.
Unfortunately, Fethry's eagerness to better Donald is so extreme that it causes him to neglect the downside of his craze of the moment. Donald must be enjoying this just as much as Fethry is, right? And if Donald isn't enjoying things at present, he will soon, right? Right...
Fethry wants to improve Donald because he likes and admires him, at least up to a point. Fethry feels Donald has many good qualities and lots of potential, and only really wishes to help Donald explore the many possibilities that are open to him. It's just that Fethry is a little too looney to realize that what he's casually treating as "possibilities" aren't just hobbies, but continued exposure to chaos!
From Donald's side...
Like a lot of other people, Donald finds Fethry incredibly annoying and stubborn. Fethry is forever convinced that his craze of the moment is one that the world should share. Donald has had his life upset more than once by Fethry's insistence that Donald conform to Fethry's ways. The fact that he's hanging around all the time like the houseguest who never leaves only makes things worse. Fethry is perhaps sick-and-tired Donald's greatest continuing source of irritation.
Yet there's a remarkable flip side to all of this. For Donald realizes that Fethry is not motivated by malice. He simply wants to 'improve' Donald's life - and for this reason, Donald cannot bring himself to hate Fethry in quite the same way he might hate Gladstone Gander. Even when Donald chases Fethry off into the sunset at the close of a story, he's not chasing an enemy, for an enemy is someone you always hate, rather than occasionally hate (and an enemy hates you, too).
Being unable to wholeheartedly hate Fethry only makes Donald feel more impotent when Fethry causes him grief.
From both perspectives:
In the past, some stories pairing Donald and Fethry didn't perform the pairing to either character's advantage. Sometimes they made Donald remarkably boring, so that Fethry unnecessarily stole the show. Or worse, they had Donald and Fethry act identically, so that neither character came off as fully himself.
Why fall prey to such problems? Donald has pride, a temper, and an ego, so if he objects to something Fethry does, he won't just sit there - he'll react in any number of ways. He might angrily try to correct the the situation (and make it worse). He might genteelly try to set an example, as if dealing with a child (and end up looking more childish). Or, if Donald is feeling mischievous, he might even try to have fun with Fethry's wrongheadedness (for example, trying to scare Fethry with ladders and black cats if superstition is the obsession of the week). You can see where this is going, can't you?