Well if he's about natural selection through war and fighting,
perhaps a Bull Elk would be a symbolic fit?

Within bull elk circles males will often fight with their antlers to achieve dominance within the circle, leading to elk with larger and larger antlers as the generations progress, thus representing natural selection.
The size of his antlers could also represent how powerful he is at any given moment/how much war is currently being waged within Nuverta. With massive antlers representing loads of war being waged, and his antlers shedding when peace is made between rival areas.

Perhaps dedicated follows could even carve his fallen antlers into weapons or religious items.

I recommend this. Moose are creatures that I don’t want to mess with. Massive and the growth of anthers would be best represented in power. Shed when peace is made or defeated.

What would you think about something like a hyena/gnoll kind of figure as well? Might fit the war theme a bit better but it almost too much where it doesnt counterbalance nature as much? I dunno aa.

That could be cool! But I do agree that a hyena might seem far more war than nature. Maybe a hyena hybrid of some kind might help emphasis the nature aspect?
Also a hyena would be very fitting if his followers are very closely knit, or if he has an entourage of some kind, as hyenas are known for fighting in packs.
So it definitely would be important to consider whether he's more about individualism or collectivism.

I do like the idea of a elk/cervine of some kind! It was one of my main ideas actually tho I was also considering a deer for Melissia so really depends there as well. I will definitely consider it and will ahve to find a decent artist to bring it to life !

In terms of analogues for a bear, the boar is a pretty good option. They and their tusks have often been associated with war or the conflict with nature or in nature. Their also a good portrayal of the savagery of nature or at least their framed that way in common media, the bullfango from the monster hunter games for example or its bigger version the bulldrome.

If you want to go more of a carnivore route the lion is another good choice as they can be very territorial with each other. The lion is frequently used to represent those skilled in combat or war Richard the lion-heart or even the term lionhearted.

Since your dealing with essentially a god of your world you could easily blend some their features together into a chimera to represent the different aspects of nature and war as it is a rather wide spectrum. It would also give you some freedom to change up his appearance every now and again.

I probably wouldn't go straight to the typical multi headed version of a chimera. To me a chimera is more about mixing and matching the feature of different animals and multiple heads can be a bit of challenge/nightmare for artists.

Sorry if I went a little overboard here, i love this kind of world building stuff. I hope this helps a little. Personally i think a bear, boar, lion hybrid deity of war and nature would be both terrifying and inspiring for those who worship or serve it while representing the many faces/aspects of nature and war.

I was actually already going for a Lion for the god of Hope/Justice due to the more kingly and righteous identity associated with lions. The chimera idea is actually very interesting though!

The boar seems like an interesting compromise so I may do stuff with it, I was also thinking a hyena due to their battling spirit and their ability to survive/feast on anything they find.

A hyena now that an interesting and cool choice and not something you see too often, they do a lot more then scavenge and are actually scary good pack hunters. Now that i think about their actually a great embodiment of nature since they are a vital part of the savanna ecosystem.
They can actually completely devour a kill not even leaving bones behind, which personifies the idea of anything goes in war and the idea of leaving nothing but a trail of blood in its wake.

If you mixed that with the traits of a boar it would certainly make up for the hyenas general smaller size and lack of strength on its own. Yeah I can see that working for a god of war, a really buff hyena with imposing tusks dressed in armoured animal pelts and welding a bunch of jagged primitive axes and spears. Dam now I've got another awesome OC idea rolling around in my head and and no ability to draw it!

I feel you there, I only have the ability to write, curses !