Literary devices include both elements and techniques. Literary elements are things that must have a place in all stories: form, structure, characters, setting, point of view, etc. "Rikki-tikki-tavi" is a variation on the form of a fable. A fable is a short story that teaches a lesson through the exploits of animals that talk, have personalities, and have adventures in which good overcomes evil or in which some other virtue is taught. Fables are not allegories because the animal does not represent the virtue being taught (e.g., allegory: "Wisdom the mouse spoke to Sloppy the worm ...").
The structure begins with one of Darzee's songs and ends with another that praises Rikki-tikki's victory. The setting is a garden of a small home, or bungalow, in India, where Kipling was born to parents who were in Christian ministry. The characters include three humans, whom Rikki-tikki protects, and various birds and animals living in the garden. The point of view is that of an external third person narrator who tells the story from a limited perspective that is restricted to what Rikki-tikki experiences:
When he revived, he was lying in the hot sun on the middle of a garden path, very draggled indeed, and a small boy was [speaking] ....
as Rikki-tikki stole in by the masonry curb where the bath is put, he heard Nag and Nagaina whispering together outside in the moonlight.
Literary techniques are optional choices author's can make about how to tell their story. These techniques may include things like symbolism, simile, metaphor, personification, etc. One technique Kipling chose is hyperbole, which exaggerates statements or qualities to heighten the effect of the narrative. An example of hyperbole (exaggeration) is when Rikki-tikki says:
There are more things to find out about in this house, ... than all my family could find out in all their lives.
There is also a grand example of the technique of onomatopoeia, which is words that represent sounds, like "the rocket went boom boom," or "the cat went phfffft phffft." Kipling uses onomatopoeia in describing Rikki-tikki-tavi, while, incidentally, revealing the source of his name:
his war-cry, as he scuttled through the long grass, was: "Rikk-tikk-tikki-tikki-tchk!"
As another example of literary techniques, even though the story is a variation of a fable (fables don't always have human characters), Kipling also employs personification, which gives human characteristics and thoughts to animals. Personification is employed when the narrator says Rikki-tikki "hopes," which is a human feeling:
[Rikki-tikki] sat on all their laps one after the other, because every well-brought-up mongoose always hopes to be a house-mongoose some day and have rooms to run about in, ....