My trilogy has Fenrisulfr, an evil monstrosity from another dimension, as its primary antagonist. His characterisation draws inspiration from Nyarlathotep and Sauron. It is responsible for all the bad things that happen in the series, as well as the actions of several antagonists eldritch abomination. Fenrisulfr appears in dreams as loved ones or religious deities and tries to convince them to find ancient weapons called Divine Tools. These tools form an interdimensional portal that allows Fenrisulfr escape from a black hole. In return, they grant their deepest wishes. Fenrisulfr attempts to persuade the protagonist to satisfy his selfish needs and hold on to his nihilistic view, while appearing as a monstrous dog to him.

Your description of Fen… however, I don’t think it is motivated by a desire for death. It is easy to see a large part of life, other than plants, as destructive, virulent, parasitic and destructive. Keep following your plan. You will end up with something strange by the logic of your plan, and no compassion for organics. The “evil” that we know is the most shocking. –

Eldritch Abomination Ludi

There are a lot of references made to serpentine entities. Is there a reason why this motif leaps to the wolf? It is just so that you can use Fenris as your name? –

Harris

It is not possible to accurately write an Eldritch Abomination. You must understand them in order to write them accurately. They are too complex for human understanding and have been the subject of madness in all historical attempts to understand them. –

Mr.Mindor

However, many Eldritch abominations from Lovercraft’s lore can make people go insane just by being there. Cthulhu’s playmates can turn your brain into pudding and make you crazy by just lifting a finger. However, it is never clear if this is an intentional act or a side effect. The terrible randomness of it all creates cosmic horror that questions our sense of cause and effect.

Check out this link eldritch abomination on Worldbuilding’s stackexchange: Link

The point I am trying to make is that although we can synthesize Fenrisulfr’s goal of “destroying life”, we shouldn’t stop there. What is side profile the point of wanting that? What is his plan? The more we don’t know, the more difficult it will be for him to comprehend.

Both the reader and the characters should question whether it is trying to kill life. Fenrisulfr can sometimes produce unexplainable or counter-intuitive effects. This could include giving power to an untinted character or taking part in defeating a human villain or dismantling a dictator during a killing spree …).