I don't see any way of Tiber Septim even coming close to winning this fight.

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Let's go through the reasons why:

D.O.G: Simple enough, this being devourers godly essence/souls and absorbs their power. The worm is an ambush predator that lives in its own pocket dimension. When it wishes to hunt or is called upon by Yharim, the beast can easily appear anywhere and at any time. This combatant is the hard-counter to Tiber Septims only way of winning, the Numidium. All D.O.G would have to do is appear quickly, devourer its power source, and make it completely useless.

Yharon: An extremely powerful dragon meant to be fought after D.O.G. He is supposedly strong enough to completely destroy an entire rainforest by himself instantly, but takes care not to while fighting the Calamity Terrarian. Using this power he could easily destroy thousands of Tiber Septim's troops.

While Yharon comes after D.O.G (stronger in terms of defenses), his attacks are not as strong as D.O.G's.

Draedon: This character is mostly unknown and doesn't have a wiki page about him. What is known is that he made machines that surpassed gods. The Exo Mechs, which, given their names, surpassed the Greek Gods Apollo, Artemis, Ares, Thanatos, and Hypnos. He is also strong enough that even an endgame Calamity Terrarian can't kill him.

He is also to have stated himself that he has traveled the cosmos before and was the one that developed Cosmic Metal, which is what the D.O.G's armor is made of.

Calamitas: Powerful enough to evaporate an entire sea kingdom with her spells at a younger age and considered to be mostly unchained except for when she has to deal with Yharim.

Finally, Yharim: Like Draedon, not much is actually known about him. What is known is that he is insanely powerful, far stronger than the vanilla Terrarian and far stronger than Calamitas, D.O.G, Yharon, and Draedon.