When writing a essay, there is usually a "default" guideline to writing one. You don't really have to follow the format, but it's a good starting point to getting your point across. It can be a serious essay, or a funny one. It doesn't really matter what type is used, but there is a normal guideline for what a good essay should have.
A normal essay usually have about 5 paragraphs. There can be more depending on the amount of content on the paper. The first is an introduction, the next three are content (body) paragraphs, and the last one a conclusion. I assume you know that already.
I always use this guideline when writing a essay. I don't think that essays should be in a strict format, but either way you write, it always seems to fall to the default setting. Your body is the "core" of the essay, which includes your reasoning for your opinion. Without hard based facts or research in the body, the essay will be weak, and won't get your point across.
However, not everyone will follow this guideline. I just think it's a good starting point, especially for those who have trouble writing good essays. I don't always write the best essay, but I try to follow the general guideline, which is what I mentioned eariler. The seriousness of the essay depends highly on the topic at hand.
Overall, I just wrote this post by using the guideline. This is the conclusion, in case you're wondering.

But you get the general idea, right? As long as you have a strong opinion with good reasons to support it, it doesn't really matter what "format" is used (descriptive, cause / effect, narrative, etc.), or what your style is (sad, funny, serious) as all types of essays will follow the simple guideline. I hope that answers your question.
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By the way, I mention the guideline because it's good for people to know how to have good essays. To answer your question in a nutshell, though, an essay can have any style you want, as long as it's appropriate to have that style.
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| quote: |
| In your 'essay', I just needed to read the conclusion. |
Cheater!

That's like reading the last chapter of a book before reading the rest. You've spoiled the surprise.