I don't remember if I posted this before, but I thought of a pretty good Modern Fiction vs Mythology MU.
Dimitri Alexandre Blaiddyd vs Cú Chulainn
(Fire Emblem vs Ulster Cycle)
Both are legendary heroes with divine origins (Dimitri is a descendant of Blaiddyd of the Ten Elites, giving him Nabatean blood. Meanwhile, Cú is both the incarnation and son the Irish god Lugh)
Both lived in countries split into multiple territories (Fódlan was split into the Adrestian Empire, Holy Kingdom of Faerghus and Leicester Alliance. Ireland is split into four provinces: Ulster, Munster, Connacht and Leinster)
Both wield legendary spears carved from the bones of supernatural beasts (Areadbhar coming from a Dragon and Gáe Bulg coming from a Sea Monster), which are known to be incredibly deadly (Areadbhar can utilize Atrocity to deal effective damage against any enemy while Gáe Bulg grows barbs within one's body when thrown like a Javelin)
Each became known by a nickname based on an animal (Dimitri was nicknamed The Boar Prince, while "Cú Chulainn" literally translates to "Culann's hound")
Both at one point met another warrior who they befriended (Edelgard and Ferdiad), but many years later would be forced to kill in a war
Both are known for sometimes giving into a form of madness during battle (Dimitri getting his nickname of "Boar" from this, and Cú doing so via "Warp-spasms")
Both of them are able to continue fighting even after having taken immense damage (Even after a massive battle, Dimitri was able to keep chasing fighting and after Edelgard until he eventually collapsed from exhaustion. Meanwhile, Cú famously was able to continue fighting against an army even when fatally wounded with a magic spear)
I used a Fate render for Cú since he's the only one who has any renders that really fit Dimitri at all. Smite Cú dosn't have any renders that I can find and SMT Cú dosn't really mesh with Fire Emblem's art style that well. As far as I can tell, Fate Cú has enough differences from the mythological figure to be a worse matchup for Dimitri, so that's neat.