OK cool, that's good to know . You might enjoy this (and the site generally): allthetropes.org/wiki/Disenchantment
I added all these tropes myself, after watching the show and taking notes. I'm sure there are many, many more tropes in the show but this gives you an idea. :)
I didn't read too much into the scene beyond it being an amusing lamp-shade, possibly even an ex machina type device (an unexpected way to resolve the problem of how to get rid of the vikings).
Deconstruction is useful if you want to see all the separate moving parts - and how they work individually and together. Ultimately, we enjoy something as a whole, and when we analyse it we can reduce it, but it's important to remember the "whole" from which the parts came. Same applies to science, the world, anything really. (Another analogy is an autopsy of a living being ha)
As for Elfo - he is a fun character for sure. His 'arc' sees him become the opposite of what he was, so the trope of "wussy elf" is inverted when he becomes the "most badass elf to ever live". Not only that, but he goes from "naive and innocent" to "worldly wise". This is just some of the fun that the writer's had behind the scenes, making the characters do unexpected things. It's like Luci: he may be a "demon", but he is actually helpful, and is guiding Bean towards her destiny.
The show is making fun of otherwise serious genres and it does that by having all the characters embody tropes which are deconstructed and then played with - that's how come it works. Not everyone has had a look under the hood, but it's fascinating and all the more entertaining when you do, imo.